The blocked resources are not generally a problem. These messages are just informational most of the time. These messages are not why your site is deemed to be mobile unfriendly since they are not included in the test. In fact, you can just plain ignore blocked resources unless they are not intended to be blocked. Since you are running WP and these are in
/wp-contains folders, these are likely blocked by design and not a problem for you to fix.
You want to log into your Google Webmaster Tools (search console) account and migrate to Search Traffic -> Mobile Usability. At the bottom of this page, you will see a short list of issues found. To the right, you will see a button with
>>. Click each one one at a time. You will see a list of pages that have failed the mobility test. Often, these have failed for the same reasons. Click any of the pages. You will see several options including Check Live Version Fix the page and use this option to test if your fix passes the test. Do this for a same set of pages. You will likely find that you only have a few minor things that effect all of these pages and that a few quick fixes can solve your problems. Work through enough of the various pages to get a good feel of what errors you have and that you have indeed fixed your problems. You will not likely have to test all of the pages- just a good sample.
When fixing this problem, you will not be working with your robots.txt file, but rather HTML and your CSS (style) file. Most of your work will likely be in your CSS file.