javascript – How to update list item using id in Sharepoint 2016 using rest api

I have two lists ‘a’ and ‘b’ with same titles but different ids. I retrieve the title from ‘a’ list to a html page. And, there is a ‘b’ list. Here, both the lists have different ids but has same titles (same items). I have created a variable count to increment the count value in Count column in b list. Now my idea is to update the count value of that clicked item from the html page in the ‘b’ list. Any solutions/ suggestions or help from you would be greatly appreciated!

Retrieving the title from ‘a’ list to a html page:

function xyz() {

    var resturl = _spPageContextInfo.webAbsoluteUrl + "/_api/web/lists/getbytitle('a')/items?$top=1000";

    $.ajax({

        url: resturl,
        method: "GET",
        headers: { "Accept": "application/json; odata=verbose" },

        success: function (data) {

            var lnt = data.d.results.length;
            var name = "";
            var cntlnks = "";
            var iconurl = "";

            for (var i = 0; i < lnt; i++) {

                if (data.d.results(i).Title == "MGT") {
                    name = data.d.results(i).Name;
                    itemid = data.d.results(i).ID;
                    cntlnks = data.d.results(i).ContentLinks;
                    iconurl = data.d.results(i).Iconurl;
                  
                    if (data.d.results(i).Phasenumber == 1) {
                        if (data.d.results(i).Phasegroup == "g") {

                            $("#mgd1").append('<div class="rowAlign"><img src= "https://sharepoint.stackexchange.com/+ iconurl +" class="groupingIcon" /><p class="listedItems" ><a href=' + cntlnks + ' target="_blank"  onclick="myFunc(this);" value="' + name + ' ' + itemid + '">' + name + '</a></p></div></ br>')
                        }

                        if (data.d.results(i).Phasegroup == "t") {
                            $("#mgt1").append('<div class="rowAlign"><img src= "https://sharepoint.stackexchange.com/+ iconurl +" class="groupingIcon" /><p class="listedItems"><a href=' + cntlnks + ' target="_blank">' + name + '</a></p></div></ br>')
                        }

                        if (data.d.results(i).Phasegroup == "s") {
                            $("#mgs1").append('<div class="rowAlign"><img src= "https://sharepoint.stackexchange.com/+ iconurl +" class="groupingIcon" /><p class="listedItems"><a href=' + cntlnks + ' target="_blank">' + name + '</a></p></div></ br>')
                        }
                    }
                    if (data.d.results(i).Phasenumber == 2) {
                        if (data.d.results(i).Phasegroup == "g") {

                            $("#mgd2").append('<div class="rowAlign"><img src= "https://sharepoint.stackexchange.com/+ iconurl +" class="groupingIcon" /><p class="listedItems"><a href=' + cntlnks + ' target="_blank">' + name + '</a></p></div></ br>')
                        }

                        if (data.d.results(i).Phasegroup == "t") {

                            $("#mgt2").append('<div class="rowAlign"><img src= "https://sharepoint.stackexchange.com/+ iconurl +" class="groupingIcon" /><p class="listedItems"><a href=' + cntlnks + ' target="_blank">' + name + '</a></p></div></ br>')
                        }

                        if (data.d.results(i).Phasegroup == "s") {

                            $("#mgs2").append('<div class="rowAlign"><img src= "https://sharepoint.stackexchange.com/+ iconurl +" class="groupingIcon" /><p class="listedItems"><a href=' + cntlnks + ' target="_blank">' + name + '</a></p></div></ br>')
                        }
                    }
                    if (data.d.results(i).Phasenumber == 3) {
                        if (data.d.results(i).Phasegroup == "g") {
                            $("#mgd3").append('<div class="rowAlign"><img src= "https://sharepoint.stackexchange.com/+ iconurl +" class="groupingIcon" /><p class="listedItems"><a href=' + cntlnks + ' target="_blank">' + name + '</a></p></div></ br>')
                        }

                        if (data.d.results(i).Phasegroup == "t") {
                            $("#mgt3").append('<div class="rowAlign"><img src= "https://sharepoint.stackexchange.com/+ iconurl +" class="groupingIcon" /><p class="listedItems"><a href=' + cntlnks + ' target="_blank">' + name + '</a></p></div></ br>')
                        }

                        if (data.d.results(i).Phasegroup == "s") {
                            $("#mgs3").append('<div class="rowAlign"><img src= "https://sharepoint.stackexchange.com/+ iconurl +" class="groupingIcon" /><p class="listedItems"><a href=' + cntlnks + ' target="_blank">' + name + '</a></p></div></ br>')
                        }
                    }
                }
            }
        },

        error: function (data) {
            console.log(data.responseJSON.error);
        }
    });
}


function myFunc(lnk) {
    let val = lnk.getAttribute('value');   
    console.log(val);
    updateItems(val);
}

Updating list item count value in b list:

var count = 0;

function updateItems() {

count = count + 1;

var resturl = _spPageContextInfo.webAbsoluteUrl + "/_api/web/lists/GetByTitle('b')/getItemById(1)";
var itemType = GetItemTypeForListName('b');

    $.ajax({
           url: resturl,
           type: "POST",
           data: JSON.stringify({'__metadata': { 'type': itemType }, 'Count': count }),
           headers: {
           "accept":"application/json;odata=verbose",
           "content-type": "application/json;odata=verbose",
           "X-RequestDigest":$("#__REQUESTDIGEST").val(),
           "X-HTTP-Method": "MERGE",
           "IF-MATCH":"*"
            },
            
    success: onSuccess,
    error: onError
    });

   function onSuccess(data) {
   alert('List Item Updated');
   }

   function onError(error) {
   alert(JSON.stringify(error));
   }

   function GetItemTypeForListName(name) {
   return "SP.Data." + name.charAt(0).toUpperCase() + name.split(" ").join("").slice(1) + "ListItem";
   }
}