ya mean getting the rubber groove on the metal lip! just hafta bend the rubber slightly to open the groove and work along a bit at a time - might use a small putty knife to help open it as you go
the ends of the rubber should be at the back, center, so just start there w/ one end and work around - if it wasn't a tight fit it wouldn't stay there - the only way is like highwayman sez, glue the headliner in first, then struggle calmly w/ the rubber and it will go
Bill