Window Seal - Coming Lose



The black strip that runs along the bottom of the window and the door on the drivers side of the car is not as tight as the passenger side. The seal slightly comes away from the door after time and if i use the window then the glass will pull it away from the door (not fully so it cant full off). Anyway, this is annoying so how can I fix it?

I reset the other seal (rear window) by soaking it in kettle water. However this seal seems more plasticy than rubber so im unsure if this trick would work.

Any advice much appreciated. Thanks.