Screen time password
How do I reset the screen time password without the old password?. I purchased the phone from someone and everything was fine and legit but they don’t even know the password
Make sure to choose a passcode that's different from the passcode you use to unlock your device. If you can't remember a restrictions passcode that you set on a previous version of iOS or iPadOS, or you forgot your Screen Time passcode, you need to erase your device, then set it up as a new device to remove the passcode. Restoring your device from a backup won't remove your passcode.
Prevent in-app purchases from the App Store - Apple Support