Flip Gone Wrong

Tanner Braungardt is out for a drive in Kansas with his best friend Erin, who he secretly likes. It starts to rain, and the weather takes a turn for the worse. The tornado sirens go off, and they know they need to take cover somewhere. The only problem is, they're in the middle of nowhere. Tanner pulls into the first driveway he sees. Him and Erin run to the door, but nobody is home. They see the storm cellar doors in the yard, and pry them open. They get inside, and shut the doors, hoping the storm will pass quickly. Tanner tries to keep Erin entertained because she's scared, and attempts a backflip. He hits the ceiling, and falls hard, hurting his ankle really bad. When the storm passes, Erin can't get the doors open, and Tanner can't stand up. Neither of them have a phone signal. How will they get out?