For security reasons, changing passwords is a common practice among users. After changing your password with the provider, you'll need to update the synced passwords on your iPhone, iPad, and iPod Touch to ensure their functionality.
Changing Email Password on iPhone, iPad:
Step 1: Go to the Settings menu.
Step 2: Select Mail, Contacts, Calendars.
Step 3 : Click on the Mail account for which you've recently changed the password.
Step 4 : In the Account section displaying your Mail information, delete the password in the Password field and enter your new password.
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So, you've successfully changed your email password on iPhone. The process for iPad and iPod Touch is similar. Additionally, there are apps available to help you manage your emails directly on your iPhone, such as Gmail For iOS and Inky Mail for iOS.