Lost file association (RAR)

G'day folks. I'v developed an issue where my RAR filetype has started defaulting to notepad for some reason. Is there a way to restore an opus default assocation or somewhere where the code to replace the 'faulty' existing references can be found??

Cheers and thanks!!
Grant

[Make RAR, 7z, ISO, etc. files open in Opus on double-click)