Password change
How do I change my Apple ID password?
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If you know the current password.
What to do after you change your Apple ID or password - Apple Support - I suggest doing this before you change your Apple ID or password.
If you forgot the Apple ID (iCloud) password, enter the Apple (iCloud) ID, and click Forgot Password. See if you can get a Rescue or Notification email option if necessary. Link to contact Apple Support at the end of the 2nd article.