If you know the passcode, go to Settings
Tap Face ID & Passcode or Touch ID & Passcode
Enter the current passcode
Tap Change Passcode
Enter the current passcode again
Enter a new passcode
Confirm the new passcode
If you forgot the passcode, put the iPad into recovery mode
Connect the iPad to a computer
Open Finder on Mac or iTunes on Windows or older macOS
Force restart the iPad
Keep holding until the recovery mode screen appears
Choose Restore when prompted
Wait for the restore to finish
Set up the iPad again
Restore from a backup if available
If Find My is enabled, use iCloud
Go to iCloud.com/find
Sign in with your Apple ID
Select the iPad
Choose Erase iPad
Set up the iPad again
Restore from a backup if available