I have looked at cia tools etc, but still not been able to figure out how to do it, hopefully someone here will know
I believe that you have to open your CIA on a hex editor and look for the line that has the game ID. Other than that, there isn't any CIA tools that really do it.
https://gbatemp.net/threads/tutorial-how-to-decrypt-extract-rebuild-a-cia.388677/ . Follow the guide and decrypt and extract the cia. Then go to the "Editing" section and follow how to change the TitleID. From there just rebuild the cia again.
