Hi, suppose I have a metal plate in between two parallel plates(the upper plate at 1V and the lower at ground(0V)); then how do we find the charge induced on the metal surface due to the capacitor plates?

I modeled two parallel plates of material PEC and kept another metal plate in between these plates using CST Studio Suite. Then I provided a potential of 1V to the upper plate and 0V to the lower plate and simulated using the E-Static solver. I got the results, and they match the theoretical values. But I got the total charge and the total E-field energy. Then, I kept a metal disk(same PEC material) in between these plates and simulated again. I want to find the charge induced on the metal disk due to the parallel plates. How do I do that in CST? I have attached a figure depicting the scenario. In the figure I need to find the 'Q' marked as "?".

Please help me with this.

(PEC=perfect electric conductor)