Is it the door lock itself behind the metal panel you have brought?
No its is the section on the right hand side which holds the door latch when you close the door.
Ok if its the plastic plate then there will be a door lock behind there so when you refit the screws it holds both the plate and door lock on and that's what the screws go into.
As the screws are not screwing into anything it sounds like the door lock has dropped.
What you need to do is make sure its unplugged and remove the top.
From there look down the front on the inside on the right and you should see the door lock.
Reach down in there and hold the door lock in place just behind the plate and then when you screws the plastic plate back on it will screw into the door lock and that will hold it all in place.
Let me know how it goes.