It won’t let me reset my Apple ID password
How do I reset my Apple ID passsword
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Exactly how you change your password depends upon the equipment you have. Click on this link to learn how to 'Change your Apple ID password' --> Change your Apple ID password - Apple Support
You said it won't let you which unfortunately does not tell us much other than you are having some sort of problem. Knowing the exact error message and problem description would speed resolution.