Access Form1 Control from Form2 Control

Question

I am Doing Notpad at the moment.

I placed a richTextBox in Form1 and textbox and a button in Form2.

When I press Find in form1, It goes to the Form2.

I need help from you from here.

when I enter a string in textBoxand press button1  in form2  , I want the  function of searching  string in richTextBox in Form1.

if it found a string , highlights the line.

please help me.