Replacing seal on garage door

Hello;

I need to replace the seal on my garage door. The seal slides into two grooves (called "T-ends", I think) on a retainer strip, which is in turn screwed into the bottom of the garage door.

Right now the screws are screwed in from the bottom, so that the seal covers the heads of the screws. The seal is easily removable, but I'm not sure how to insert a new seal. Do I remove the retainer, slide the seal into the retainer, and then screw the retainer onto the door with the screws facing the opposite direction (pointed ends towards seal)?

Or would it be possible to leave the retainer on the door, and slide the seal onto the retainer from either side of the door (there's about

Thanks in advance.