I would like to change the icon for a mimetype. I followed the instructions of this post, however it does not seem to work. What would be the pop!os method to change icons?

uname -a
Linux pop-os 5.4.0-7634-generic #38~1596560323~20.04~7719dbd-Ubuntu SMP Tue Aug 4 19:12:34 UTC 2 x86_64 x86_64 x86_64 GNU/Linux