There is a knack of getting them back on. Get the key and work out which way round it goes and make sure that everything is located properly to the key.
Then get your better half to turn the laptop upside down and hold tight and then firmly push up to locate the key.
If they are half on half off get a jewellers screwdriver and ease them off completely its virtually impossible to get them back on without breaking one of the wee plastic lugs.
I presume you used the squirty straw attachment to jet blast under them.