Okay, wanted to get that part out there. The trim should be aligned to proper position end to end, then press the bottom side tight to the body and while holding it tight "pop" the top side of the trim onto the clip. You will likely have to do this near each trim clip. Alternately, if the clips stay in the molding they may fasten inside the body with a nut, so those don't get the specified treatment, but should be the first positioned/seated if there.
If you can post a pic of the clip, we can be of more specific help.