What kind of glue, is it still tacky like tape residue? Some mineral spirits or wd-40 on a wipe will usually get that kind. If it's water base like elmer's maybe soapy water, again on a damp towel. Silicone will rub off usually. Epoxy or super glue- no luck. You could also try a little toothpaste as a mild abrasive and polish. Turn the tablet off and don't let water get into it. (of course)