Remove the roller track where the top of the bifold door hangs using a screwdriver. After the roller track is removed from the wall, it can be unhooked from the door.
Unscrew the wheels at the top of the bifold door and remove it.
Pull the door so that it is open and the two panels are stretched flat. You are now facing the part of the door that faces the closet.
Screw a mending brace across the two panels about three to four inches from the top of the door using screws and an electric drill. Mending braces are metal rectangles with holes punched on either end.