What I've done successfully in the past: make sure there are sufficient clips in good condition alongside the metal rim. Then push the strip so that it starts to engage with the clips properly. Then, for the final few millimeters, a couple of fast firm blows with the flat hand, to seat the trim onto the clips. As you hit the strip, you can see it seating. There is probably a better, less 'violent' way, but this has worked for me.