how to reset screen time passcode ios 13

Follow the instructions in this Apple support article—>If you forgot the passcode for your iPhone, iPad, or iPod touch, or your device is disabled - Apple Support. After restoring the phone as described, do not restore your backup as it will also restore the screen time passcode.

Just to add one note to Lawrence's great reply: you CAN restore from a back up, but it will have to be one that does not have the screen time passcode on there, otherwise, as Lawrence said, it will bring it back. You probably won't be able to tell if you have it on the back up until you restore it and then check. Best of luck.