You will need to remove the whole door and then put it back on. If your oven is the same as mine (Zanussi FM 21) you will need to open the door fully and use a coin to move the two retaining disc 90 degrees clockwise. Then move the door halfway up and pull from the hinges upwards to remove the door. Then to replace the door, grasp the two hinges on either side together and hook the top hinge into the top slot so that the hook is engaged with the roller. then drop the lower hinge into the lower slot. Bring the door back down and turn the disc back to their original position. Hope that helps.
Matthew Beevor, October 2004