It's really hard to reassemble. I've only done this once but if I remember correctly, the two H shaped pieces fit together to form an X shape when viewed from the side.
There should be tiny pivot points at the top, these should be carefully clipped into the keytop. After this, the whole assembly should fit into two little slider type sections on the keyboard. A lot of patience is required unless you are very lucky. Be very careful that you don't snap the tiny tabs at the top & bottom on the H sections when reassembling because if these break then the key is useless.
It's a nasty job & difficult to explain exactly how to do it - patience & perspiration was the way I finally managed it . . . .
