To repair a sagging automobile headliner, take out the dome light; disconnect its wires; remove the headliner's trim, visors, seat belt hardware, rearview mirror, and board of the headliner; and sand the board. Glue the replacement fabric to the board, replace the board in the vehicle, and reassemble all the parts removed. Use a repair kit meant for headliners for this purpose.
Begin repairing a sagging automobile headliner by taking out the dome light located on the car's ceiling. To do this, gently press and detach the bulb's plastic cover, undo the light's screws, and detach the wires from the snap connectors.
To take out the trim, pry it off using a screwdriver with a flat head. Alternatively, lower the trim just enough to take out the headliner board. With the same screwdriver, detach the plastic cover of the hardware of the seat belt. With a 3/16-inch wrench for spark plugs, undo the bolts; and with a torx screwdriver, take out the hangers and visors. If required, detach the rearview mirror.
Have someone hold the trim of the headliner out of the way, and pull its board out. Remove the board's fabric, and sand the board to take out imperfections and old adhesive. Apply fresh glue to the board following the instructions provided with the headliner repair kit, lay the replacement fabric over it, and smooth out any wrinkles.
Air-dry the adhesive as instructed in the repair kit, and re-fit the board in the car. Finally, replace the trim, visors, hangers, and seat belt hardware, as well as the rearview mirror and the dome light.