Use w3 Total Cache for Defer Parsing
w3cache plugin have built-in option to defer the JS files, you can do this in Minify section of the plugin, open Minify Page and then jump to JS section, here choose “Non-Blocking – Defer” in embed option as shown in image and save the settings, clear all your caches and check your site again with Google Page speed or GTMetrix.
This option will work for most of the people, if not then try the next one.
Hard coding your Theme
Some themes have built in JS handlers so they can be used to defer JS parsing, you can simply do it by adding the following given code in active theme Function.php file before closing of PHP tag (?>)
This will most probably solve your issue, if not try next.
Eliminating Render Blocking Scripts Manually
If you have some external scripts and they are causing the issue, then you can simply defer them by adding few tags to them, here’s how:
Just add defer tag to your scripts as shown above and it will do the rest.
If everything fails for you then you need a developer to code your site manually, there are a lot of wordpress developers avilable on Fiverr at low cost, just hire any trusted seller from here or from freelancer and they will do it, if you got any other issue, feel free to ask, I am here to solve your problem.