consider this a extension to the great answer from @guardian10
before we contact anyone I would first clean the battery connector and both screen connectors on the logic board and the parts them selfs with isopropyl alcohol to remove any microscopic dirt our human eyes can see!
also make sure there are no burned/missing/bent pins on the connectors or on the parts
also your iPhone hasn't been excessively dropped or been previously bent as the iPhone 7 has a issue where this will happen if dropped excessively or bent
hopefully this helps
any questions please ask