If you broke your installation of OMORI (meaning it doesn't work properly or at all), then you can fix your installation using Steam.

This might override (delete) mod files, so make sure you back up files you want to keep.

Save files should not be affected, but they might become unusable if they require a specific mod.

Here's how to fix your installation:

1. Open Steam
2. Right-click OMORI and choose Properties
3. On the tabs on the left, click Local files
4. Click Verify integrity of game files… This will make Steam check the files and cue an update to download fresh files from it's server if needed.