Please advise why I have to remove my personal email address to change my apple id

Hi mmm9876,

Welcome to the Apple Community.

Apple's support article "Change your Apple ID"

Says:

"If you see a message that the email address you want to use isn't available or is already in use,

check that you or a family member aren't already using that email address with a different Apple ID.

If a family member is using that email address, remove it from their account then try to use it."

Complete article: https://support.apple.com/en-us/HT202667

All the best :-)

Have you logged into your Apple ID to see if the address shows under Reachable At, as a Rescue email address, or as a Notification email address? If it is listed, you can remove/replace the email address.

Apple ID - Manage  

Apple hasn’t published any guidance for using an address again. Normally, if your e-mail address was associated with an ID in any way, for example as a Notification email address or a Rescue e-mail address, then it can't be reused as an  Apple ID email address for approximately one year. I have also seen posts that stated Apple told them there was a 30 day waiting period before the address could be used again. You will need to get another e-mail address from somewhere like AOL or Yahoo to use as your Apple ID or you can try waiting 30 days to see if that works.