How do I fix some broken thumbnail preview settings in Nautilus?

Okay, I wanted previews for psd files in Nautilus. So I tried the scripts found on this page: How to make Nautilus display .psd thumnails?

This did not work, so then I found this maintained PPA, and I decided to try that.

It did not seem to work either. But it does krita files in addition to psd so I made a krita file and that preview worked!

So I think the issue is that the first script I ran somehow messed up my settings so that the installed PPA won’t work.

Any clue on how I can reverse the effects of the first script? I don’t know enough about the internals of Linux etc to really manipulate this stuff very well. I can use Linux, and do web development but I’m not really clear on how it actually manages thumbnail settings etc. I assume that’s something that the shell does etc.