How to update contents of rich text box in form1 with values coming from form2 without closing form2?

How to update contents of rich text box in form1 with values coming from
form2 without closing form2?

I want to pass values between two Forms (c# both in active states). How
can I do it?
I have two forms: Form1 and Form2.
Form1 contains a rich text box and a button. When I click on that button,
Form2 should open and a text in rich text box should be sent to a textbox
in Form2 and Form1 should remain opened as well being on back of Form2.
Form2 contains a text box and a button where user edits a text in textbox
and when user clicks on a button then the edited text should be sent back
to the rich text box in Form1 and the Form2 should close/ stay opened and
Form1 should highlight the updated text in rich text box.
How can i do it? Can somebody help me to do this with a simple example?