See -> Use a passcode with your iPhone, iPad, or iPod touch
Use a passcode with your iPhone, iPad, or iPod touch - Apple Support (IN)
👉 and never share your passcode.
Change your Apple ID password.Â
Create a strong password for your Apple ID, It is best if your password consists of eight or more characters and include upper and lowercase letters, and at least one number. You can also add extra characters and punctuation marks to make your password even stronger.Â
Never provide your password, passcode, security questions, verification codes, recovery key or any other account security details to anyone else. Apple will never ask you for this information.
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Then see this Apple article: What to do after you change your Apple ID or password
What to do after you change your Apple ID or password - Apple Support