Update the simple MVC infrastructure database from JSON

I am new to MVC and I have inherited a framework from a previous developer, I would like to know how to update the database with the help of an external JSON. Here is the composer information for the framework:

{
"name": "simple-mvc-framework / framework",
"type": "project",
"description": "Framework for PHP 5.5+",
"homepage": "https://github.com/simple-mvc-framework/framework",
"license": "MIT",
"Authors": [
        {
            "name": "xxxxxxx",
            "email": "xxxxxxx",
            "homepage": "xxxxxxx",
            "role": "Developer"
        }
    ],
"need": {
"php": "> = 5.5.0"
}
"autoload": {
"psr-4": {"": "app /"}
}
"minimal stability": "dev"
}

I've inherited a framework from a previous developer and would like to know how to update the database with the help of an external JSON.

Road

run (& # 39; roads & # 39;);

/ ** If no itinerary found. * /
Router :: error (& # 39; Core  Error @ index & # 39;);

/ ** Enables routing to the old. * /
Router :: $ fallback = false;

/ ** Execute the corresponding routes. * /
Router :: dispatch ();

admin.php

_models['stream_settings'] = new  Models  StreamSettingsModel ();

}

public function get_checklist_config ($ isAjaxCall = FALSE)
{
$ url = & # 39; https: //www.domain.com/path-to-JSON/&#39 ;;

if (! $ isAjaxCall) {
 Helpers  Url :: redirect ($ url);
} other {
$ jsonOutput = Array ();
$ jsonOutput['url'] = $ url;
echo json_encode ($ jsonOutput);
}

}
}

JSON

{"id": 600, "field1": "test field", "field2": "test field 2"}

StreamSettingsModel

db = database :: get ();
}

function getChecklistConfig () {
// something on these lines: $ this-> db-> update (PREFIX. & # 39; stream_settings & # 39 ;, array (& # 39; get_checklist_config & # 39; => $ get_checklist_config), array (& # 39; id = id $);
}
}

I'm struggling with the PDO part, especially with the getChecklistConfig () function. How to get the JSON to update the database by following existing MVC routes?

Any help is really appreciated because I am new to this! Thank you.