Change PCB buttons for push buttons
If you remove those silver "domes" (like carving them away with an Xacto knife or equivilant) you will see the PC board contacts that get joined together when you collapse the dome.  THOSE are the contacts that you need to connect to an external switch (of whatever type). You have no assurance that the nodes you need will even appear on the bottom side of the PC board. But you have 100% assurance that they are directly under the domes.