Review this guide MacBook Air 13" Early 2015 Display Assembly Replacement. Follow the first steps to Step 3, then jump down to Step 19 to put aside the display connection to reach the screws underneath. Follow to Step 21 which points to the hinge screws that likely have loosened up (all six screws). If that didn’t solve it you’ll need to go back and follow the guide through as the lid screws are then loose. Stop at Step 26 after pulling off the display you’ll need to pulloff the black plastic clutch cover which covers the screws on the lid.
Use some clear fingernail polish around the hinge screws screw shaft just before fully tightening to help in preventing it to loosen again.