What to do if I can't answer Apple ID security questions when trying to change my Gmail?

Hi, I have an issue with my Apple ID. I am trying to change it to my main email, but I used that on an old one that isn't in use anymore. I was able to change the password but I can't do the security questions. I know the awnsers, just I likely misspelt them when I was a kid so it isn't really working

what I want to do is to disconnect my main gmail from that old ID, then connect it to my current ID

[Re-Titled by Moderator]