Reinstall the headliner to the car:

Reverse the removal steps to re-install the headliner into the car.

Start one edge over the side trim panels and then raise the headliner into position over the other side trim panels.

Re-install the sun visors, dome lamp, seat belt upper loops and any other items that were previously removed

Lightly brush the headliner to remove marks & fingerprints.

If any of the trim clips break off of the interior trim panels, you can reattach them to the panel with 2-part epoxy glue.