How to passing value to textbox in second form when object has been lunched

I have a problem.

I make project in winforms with the c#.

I have two forms. Opening with the Show() and midiContainer.

Example:

I open Form1, where I have eg. TextBox with data about Customer (Name company). I selected Customer from second Form2. I secleded value from grid. I have this data. I Can't passing value to first Form1.

I thinking first Form1 is initiated the first. How passing value to first form from second form?

I tryed use reflection. Unfortunately, doesn't solve problem.

This problem doesn't occur when use ShowDialog().

Please help me.

Kind Regards.