Wait for the oven to cool completely, then open the oven door. If the handle is completely off, pull the door from the sides of the door to open it.
Realign the handle with the door handle screw holes on the top of the door.
Attempt to install both door handle screws using a flathead screwdriver.
Remove the screw and inspect the threading if one or both of the screws will not catch the handle's threading. If the threading on the screw is damaged, replace it with an identical screw from your local hardware store. If both screws are in good condition, you will need to substitute a new door handle for the old one.