How to modify value in form 3 from form 2 in c sharp windows form application

I'm creating a simple ATM which consist of 3 forms. in form 1, it contains 3 buttons: Balance and Withdrawal. In form 2, it's the balance form when the user click the balance button. it shows the current balance which is set to 5000 as a default value and it is displayed in a text box. while in form 3, it's the withdrawal form when the user clicks the withdrawal button. it contains text box for the amount that the user wants to withdraw and an Okay button. now my question is how am I going to change the value of balance when the user withdraw?