Hello Peter,
you woudl want to start with the building block variable capacitor: https://www.mathworks.com/help/physmod/sps/ref/variablecapacitor.html?searchHighlight=variable%20capacitor&s_tid=srchtitle_variable%20capacitor_3
You'll need some simscape basics to go along with it: https://www.mathworks.com/learn/tutorials/simscape-onramp.html
Then you need to create a simulink model that controls the capacitance based on where the user is touching, and connect that up to the variable capcitors to control their capacitance.
Regards,
Joel
