Just that really. Advice from the RSPB says to give exhausted bumblebees an energy drink of sugar and a bit of water if you see one struggling.
Best to put the mixture in a bottletop and keep an eye on your stripy friend to make sure he doesn't drown. I did this today and it was lovely. The bee enjoyed it as well and flew off into a flowerbed.
I didn't know about this till very recently so thought I would spread the word and see if this nest of vipers could help save more bumblebees 