Get all the parts together as (from top to bottom): glass - stainless steel - heatbed pcb - cork sheet - mdf.

Note that the ntc is already attached to the heatbed pcb, it should be facing the cork. In order to make good contact, you may have to bury the ntc in the cork.

Take this sandwich and attach it to the frog.

In the back, this sandwich should be slightly inserted in the cubes.

In the front close the quick release to tighten up.

Connect the wire.