Gluing the headlining back in place if the headlining on the car has only sagged partially for example around the edges you could use glue to re attach it.
How to fix a sagging roof liner.
The best method you could use to fix a sagging headliner would be rejuvenating the strength of the glue that has become loose due to constant exposure to sunlight.
One of the easiest ways to put the headliner back into its place is to use glue.
How to fix sagging headliner without removing it.
Use the steam cleaner and paint roller combo.
The quick methods you can use to fix a sagging headliner 1 gluing the headlining material back in place 2.
As time passes the glue that holds the fabric of the headliner with the roof losses its power and becomes dry.
Using staple pins and hair spray 4 use clear headed twist pins 5 use the double sided tape 6 revive the adhesive with a steam cleaner.
Use pins to firm it 3.
It will best work if the fabric.