Turn the mousepad over and peel off the grip with the white plastic layer.

The white plastic layer is glued to the device only on it's edges so if you're using the ifixit head pad you only need to put it on the edges.

Be sure to peel the grip + the white plastic layer. Removing just the grip and then the plastic layer will result in a very tedious process of trying to align the grip properly.

Unscrew the 3 screws with a phillips head screwdriver

Desolder the copper leads (red circle) and open the gate of the connector (blue circle)

You can now safely take out the pcb

For reassembly simply follow the steps in reverse