HELP Save text entered in the Message section to a variable
 

Hi I am writing a complaint add-on. I have created a menu and I have written the names of the players in this menu. When a person selects the player he / she wishes to complain, a warning should be indicated in the messages section, "Write down the reason for the complaint" and the person will enter the reason for the complaint in the message section. After I have chosen the person I'm hanging out with, I can assign the reason for complaining to the message part to a variable. Please help me.