How to Override Web IDE Filetype Guessing for Syntax Highlighting?

Hi, i am trying to have Web IDE to treat some files with custom extensions (say *.myvb files) as if VB files for syntax highlighting, but i cannot find any information in the helps.

There is a page describing syntax highlighting using .gitattributes (https://docs.gitlab.com/ee/user/project/highlighting.html), but it applies to only viewing the files but not the IDE.

Is there any way to do that? Thanks!