To fix a bug or enhance a feature, you are warmly invited to go to Tiki project at Gitlab, fork the project and send a merge request.
If you do not know how to use Git or otherwise can't do this at the moment, you can submit your code here on dev.tiki.org as a patch. A patch is a regular tracker item and you can attach your patched file(s). If it's just a few lines, you can also just put the patch in the tracker item using the CODE plugin.
Please also see: Where to commit and All Patches