There are no clips or crimps but simply push on, it holds itself on but with age the plastic trim hardens and this can lead to the trims flying off because they have lost the tension on the teeth moulding inside plastic trim that holds them in place, age makes the trims brittle and crack.
Put the roll of trim in a bucket of hot water. When supple and forgotten that it was in a different shape, put it on the car and let it cool in place. Stands a better chance of fitting better and staying there.