How to change my Apple ID password?

1. Tap Settings > [your name] > Password & Security.
2. Tap Change Password.
3. Enter your current password or device passcode, then enter a new password and confirm the new password. Forgot your password?
4. Tap Change or Change Password.
5. Sign in with your new Apple ID password to access Apple features and services. 

Change your Apple ID password - Apple Support

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Here --> Change your Apple ID password

Here --> If you forgot your Apple ID password