820 window seal.

Just noticed today that the nearside strip that sits over the edge of the front window screen had somehow moved out of its place, It looks like someone has tried to lever it out of its seat down its whole length. It doesn't seem to be actually coming off the car. and it doesn't seem to hold the glass in or seal it either , but I don't want it to suddenly disappear behind me on the motorway. Can anyone advise me of the best way of putting it back to where it should be. Hotfoot