You cannot legitimately “figure out” someone else’s Screen Time passcode
If it is your device, use the Apple ID account used to set up Screen Time to reset it
On iPhone or iPad, go to Settings
Tap Screen Time
Tap Change Screen Time Passcode
Tap Forgot Passcode?
Enter the Apple ID and password associated with the Screen Time passcode
If you use Family Sharing, ask the family organizer to change or reset it
If you bought the device used, contact the previous owner to remove Screen Time restrictions
If you forgot the device passcode, use Apple’s official recovery steps for your Apple ID and device
If none of these work, contact Apple Support