How to Calculate C1?

Hi, I am asking for help because I need to find C1 in my transferfunction. Up top you have the circuit and next to it you have the graph. What is the formula to calculate C1? Thank you in advance

Hi, I am asking for help because I need to find C1 in my transferfunction. Up top you have the circuit and next to it you have the graph. What is the formula to calculate C1? Thank you in advance