You can find it in the "Local Settings" section in the settings. If you are on mobile, you have to scroll down from the settings block. Also you may need to clear caches.
Note:
These options are kept on the device and are not synchronized between devices.
Do you plan on making pull requests available on your gitea? I can imagine some people would be willing to contribute such small patches instead of making proper code changes in lemmy's main repo.
Though I of course understand if you don't want that!