You could create some public properties on your forms to hand values back and forth. Or pass the values in a method call of the form you are handing them to (this could be the form's constructor or an explicit method defined for this purpose.
Alternative, you could read about the Model-View-Controller design pattern which is intended to make this kind of behavior rather trivial. Each form is a "View" to the "Model". The "Model" is your data structure that contains all the parameters of the business operation.