The Shift key on the left side of my Logitec K330 Bluetooth keyboard came off. This is how I fixed it.
The back of the Shift key consists of a movable wire with bent feet on either end and two side-by-side squares. The Shift key clicks onto two matching squares with holes in them inside the keyboard case. Slightly to the side of each square in the housing case is a tiny block with an indentation at the top. (Note: A flashlight makes these blocks easier to see, especially with a black keyboard.) The feet on the wire fit into these indentations. Holding the key so you can read the word 'Shift,' move the wire so the legs point toward the top of the keyboard. Carefully place each wire foot into its slot and firmly push the key onto the squares.