Press down on the inner roller adjustment at the top of the bifold door to disengage the wheel from the upper track. The door will now swing outward on its own for access to the top edge.
Pull out the inner roller adjustment from the hole on the top edge of the door, using the pliers.
Push the new part into the hole and press until the inner roller adjustment seats flush with the top of the door.
Press the spring-loaded wheel on the top of the inner roller adjustment and guide the door under the top track. Release the wheel, which will snap up into the track. The door will now open and close normally.