If you have a back up I would recommend to restore the iPad using iTunes, connect your iPad to iTunes using lightening cable and click on your device on iTunes then click on restore button, this will restore your device to factory setting (also deletes everything from your iPad as well), after restore completed, depends where you have your back up, if on iTunes, leave the device connected and on the first screen it will ask you which back up do you want to restore from, choose you most recent back up, if you backed up on iCloud, disconnect the device from iTunes, go thru the set up on your iPad, and choose restore from iCloud back up, log in with your apple id and password and let it restore from that back up.