Using a wifi dry contact module (Sonoff) to increase/decrease temperature in a gas water heater touchpad
Capacitive touch sensors not have two terminals so you can't directly use a relay to simulate a button push. They work by sensing if there is a sudden but small change in touchpad capacitance (in the order of few picofarads). Since the pushbuttons are capacitive, the whole circuit board may not be mains isolated, so be careful.
It might work if you simulate a finger with some capacitance and resistance to ground, but it is impossible to know what values are good, and even the capacitance of the extra wiring can make the pushbuttons unstable.
Modifying equipment needs good understanding of the modified device, such as schematics, but it may not be enough if the touch sensing algorithm is made in software.