Need to unplug drain tube

Question

need to unplug drain tube in 2005 roper fridgeI have a Frigidaire frs26zgh. I have ice buildup in the bottom of the freezer too. I pulled everything out of the freezer including the shelves and the back panel. This exposed the cooling coils and the fan. I could see more ice and where the water was supposed to drain out the bottom to the drain pan. It was plugged. I tried to thaw it out to see if the ice was backed up in the tube, and am still waiting. When I pulled the fridge out and looked from the back I could see the pan the water was supposed to be draining in to and it was dry. How do you unplug the drain tube?