What have you tried so far?
What has or has not worked for you?
Do you have a schematic of a voltage doubler which you wish to test in simulation?
Are you interested in one that is supplied by AC? Or pulsed DC? Sine waves or square waves?
I'm working on something along the lines of this schematic :
https://www.indiabix.com/electronics-circuits/voltage-doubler/
And the Capacitance would be in 100pF and an AC supply, sine waves. How would I go about doing the simulation?