This guide is for hinge type K29. This hinge type is used in the following models:
Some colors in the pictures may differ for your model. That is fine, what matters most is the shape of the hinge piece.
The plastic hinge mechanism must be oriented as shown for it to fit onto the metal keyboard hooks.
Hook the bottom inner part of the hinge under the bottom two metal hooks on the base of the keyboard. Here we are using pliers but this can be done without tools.
Tuck the top of the hinge into place, by pressing down and inwards on the top half of the hinge, one side at a time. The top right and left sides of the plastic hinge should be hooked under the two metal loops protruding from the base of the keyboard on each side. Check that the hinge works by flexing it up and down; it should pivot easily at its axis.
Align the key on top of its place on the keyboard, and press down evenly. All four corners of the key should click into place.