How do you change your Apple ID in your phone?
How do I create a new Apple ID on my phone that has the old Apple ID
iPhone 13 Pro Max
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You can change the Mail Address for your old Apple ID by following the steps in this article:
Change your Apple ID - Apple Support
After that, there are a few more things to do:
What to do after you change your Apple ID or password - Apple Support
If you want to create a completely new Apple ID, you'll have to remove the Activation Lock before:
About Activation Lock on your Apple Watch - Apple Support
Since purchases are linked to an Apple ID, you will have to download those again for your new Apple ID, since two different Apple IDs can't be merged.