Rear view mirror - how to clip on?

[Unlight]

 Hi all, was cleaning my windscreen today, and managed to accidentally pop my rear view mirror off on the left hand side - heres a pic to show -




 Anyone know how to reattach it? It doesn't seem to click back in place, and a bit wary of pushing too hard in case I crack the windscreen!

 Any help appreciated!

[Jimble]

I'm sure it should just push on, has the mirror itself moved so it's being obstructed?