You can change the email associated with your account directly from ChatGPT settings.
To do this:
Sign in to ChatGPT.
Go to Settings → Account.
Update your email address and confirm the change.
Note: The new email must not already be linked to an active OpenAI account.
Because ChatGPT and the API Platform use the same account, updating your email in ChatGPT will also update the email used for your API account.
Learn more about changing your email address associated with your account.