Greetings Koko157,
Thank you for using Apple Support Communities. It seems like you are trying to change the email address used as your Apple ID, but it is already in use for another purpose. We would recommend you use this article to see how to change the email address used as your notification email address.
Having a rescue email address is optional but recommended if you do not have two-factor authentication or two-step verification. If you ever forget your security questions, you can use your rescue email address to reset them. We also send any account security-related notifications to your rescue email address. If you have two-factor authentication or two-step verification, you have a notification email address instead of a rescue email address and won't need to remember security questions.
- Sign in to your Apple ID account page.
- Click Edit in the Security section. You might be asked to answer one or more security questions before you continue.
- To add a rescue email address:
- Under Rescue Email, click Add an Email Address, then enter your rescue email address. We send a verification to that address. Didn't get the email?
- Enter the verification code and click Verify.
- To edit a rescue email address:
- Select Change Email Address under the address you want to edit, then enter the new address. We send a verification to that address. Didn't get the email?
- Enter the verification code and click Verify.
If you had a rescue email address on file when you upgraded to two-factor authentication or two-step verification, you can also use these steps to edit your notification email address. If you remove the notification email, you won't be able to add a new one.
- Sign in to your Apple ID account page.
- Click Edit in the Security section. You might be asked to answer one or more security questions before you continue.
- To delete a rescue email address, click
next to the address."
About your Apple ID email addresses
Please don't hesitate to let us know if the steps resolved your issue or if you need additional assistance.
Take care.