To change the linked email address, you need to unlink the current account and then add the new account.
Please follow the steps below to unlink an email address from your account:
- Tap the main menu
, select [Settings] 
> [Account]. - Tap the checkbox next to the login method to unlink it. Note that you cannot unlink if you are currently logged into Pokémon GO with that login method.
- To re-link it, tap [NOT LINKED] and follow the on-screen instructions to relink the account.
To link a Facebook, Google or Apple account to Pokémon GO, you can follow these steps:
- Tap the main menu , tap [Settings] > [Account].
- Tap the checkbox next to which account you want to link: Facebook, Google, or Apple.
- Follow the on-screen instructions to complete the setup. For detailed instructions, please refer to this help article.