ET5 Pro Levelling Probe AND Endstop

Having, hopefully, sorted the teething issues with my ET5.
I have decided to go with the hardware switch for the Z-endstop
I would like to keep the probe as well, for levelling purposes
As we know the ET series doesn’t like keeping its level stats in memory

I don’t mind doing the levelling on start up, I just hate having it hit the bed all the time, on power up
Hence the decision to install a HW Switch

Can somebody help with install?
Where do I wire the switch?
What do I need to edit in Marlin?

There is a spare socket on the ET Board, but I am assuming that is the Z_Max Endstop plug
The Probe uses the Z_Min plug

Another site I use for help has informed me I am able to use the spare plug for the HW Switch
Still waiting on what to change in Marlin