How to change icon for all files with the same extension?

[emikaadeo]

I'm using Movist as my default app for files like .mkv .avi .mp4 etc.
Movist has it's own file icon for every video file extension.
This is how icon for .mkv looks like and how Finder displays icon for every file with .mkv extension:

Looks great.

Now this is how Movist icon for .avi file looks like:

and this is how Finder displays it:

My goal is to change icon for every file with .avi extension to looks like the one from Movist app.
I've already tried https://support.apple.com/guide/mac-help/create-custom-icons-files-folders-mac-mchlp2313/mac but this solution is changing icon for only one file.
How to change icon for all of them?

 

[emikaadeo]

Well, it looks like this is a bug in macOS Catalina.
Same issue with Keka app.