The Variable Ratio Gear block in Simscape Driveline is a very abstract CVT. It allows you to represent the behavior of a CVT without needing all of the masses, spring stiffnesses, and damping values of the internal components. If you have measurements from the input and output shafts of the CVT, you could parameterize this block to mimic the behavior.
If you want to specify parameter values for internal components, you would need to create a model that has those components. You can assemble springs, dampers, masses, and use lookup tables to handle nonlinear effects. If you had a specific CVT datasheet to work from, we could point you to the closest example we have.
