Solder point for ZR button help!!

working on custom controller for my daughter who is a huge gamer despite being too weak to move, due to a terminal genetic disease. She and I play together, I use the controller and she controls two buttons via bypass cables soldered to the PCB and connected to very sensitive switches under her hands. She's actually really damn good at it too.
I've already modified the pro controller to accept switch inputs for the buttons. However, my daughter disparately wants to play Splatoon, which requires the gamepad controller (specifically the ZR button)

I have the ribbon cable for the right side controls mapped out already. The button XABY connect to the TP# noted in my attached image. However, the ZR button I need (pin 4 from top down) simply dives into the multi-layer PCB. I can't seem to find where that trace resurfaces though.

Any help would be greatly appreciated

 

mad props for being such an awesome dad!
as to your problem, you can always just scrape that bit of the mask on the via and solder on to it.