What do I do about screen popping off due to possible swollen battery

I would turn the device off and stop using it. A swelling Lithium battery can be a fire risk, and if the flexible pouch that contains it tears, there is risk of exposure to toxic lithium. Then make an appointment with apple or an Apple authorized service provider and get the battery replaced.

Use the Get Support link at the top of this page to open a case with Apple.

Got a valid warranty and insurance like AppleCare+?