What is small t rubber gasket from?

Went to repair my daughters Metro PCS LG K7 phone that she dropped. Upon opening the back, a small "T" shaped washer/gasket the size of a pencil eraser fell out. For the life of me, cant locate where it came from and cant find any schematics for this device. Anyone by any chance have a clear picture or schematics of where it goes/came from? Thanks.