Change label's text

Question

Hello,

I have form Form1 and it have some labels. When I click on one of them, it calls new pop-up form frmPopUp. This form also has Label, which text when I click it must be inserted into label's text that called form frmPopUp. Events handlers:

        public void Label_Click(object sender, System.EventArgs e)       

 {   

         Control label = (Control)sender;           

 AddPopUpForm(); 

       }

        public void frmPopUp_Label_Click(object sender, System.EventArgs e)        

{            

Control label1 = (Control)sender;           

  label.Text = label1.Text; // -->?                 

    }

I don't know how to access Label, that calls form frmPopUp and pass to it text from label, that was clicked on frmPopUp form.