Screen time password

To reset the Screen Time password on your personal iPhone follow these steps:

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1. Open the Settings app, then tap Screen Time. 
2. Tap Manage Screen Time. 
3. Tap Change Screen Time Passcode, then tap Change Screen Time Passcode again. If asked, enter the Apple Account email address and password that you used to set up the Screen Time passcode.
4. Enter a new Screen Time passcode, then enter it again to confirm. 

It’s recommended that you don’t skip adding a Screen Time Passcode Recovery. That way, if you forget your Screen Time passcode, you can use your Apple Account to reset it. If you have more than one Apple Account, you must use the same account you entered when you set up the Screen Time Passcode Recovery. 

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copied from: Change your Screen Time passcode on an iPhone or iPad - Apple Support

In case this is an iPhone for a child, only the family organiser can change or reset the code:

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1. On the family organizer or parent/guardian's device, open the Settings app, then tap Screen Time.
2. Scroll down and tap the child’s name under Family. 
3. Tap Manage Screen Time.
4. Tap Change Screen Time Passcode, then tap Change Screen Time Passcode again.
5. Enter a new Screen Time passcode, then enter it again to confirm.

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