67 Barracuda headliner install

there are some special clips under that channel . They clothes pin the headlinner into place and the channel snaps onto them also.
If you peel back the edge of the window gaskets your find teeth like anchors stamped out of the sheet metal that the headlinner is attached to.
If you search the subject here you'll find a lot of members have agreed the umbrella type headlinner install is a job for experienced pros.
Only real advise I have is cover those rear seat anchors with something or your knees will be bleeding soon. Good luck