It is possible a rivet broke causing the rear glass to sag. The fireplace will need to be disassembled and whatever the rivet was securing will have to be secured with a sheet metal screw.
Inside view of a good rivet in back right of fireplace 
Outside view of the same rivet
Tools needed:
Philips Screwdriver
Drill
Glass Suction Cup
Materials needed:
Sheet metal screws
C or L bracket
1. Power off the fireplace.
2. Remove the front glass by first removing the 2 screws securing the retaining bar.
3. Using the suction cup provided, pull the glass up first, then tip the bottom and pull towards you to remove the glass. (Note: do not use the suction cups to hold full weight of glass.)
4. Remove the fireplace media.
5. Remove the panel that the glass was sitting on.
6. Remove the screws on either side of the hearth tray.
7. Lift the hearth tray from underneath and remove. The hearth tray mount does not pull up.
8. For easier access to the back right corner, remove the six screws securing the LED bar from the body. You will need to disconnect the LED strip from the connector.
9. Remove any media that is stuck between the rear glass and the frame body.
10. Bend any bent pieces of metal with pliers, crowbar, or whatever you have on hand to the bend metal back into position.
11. Drill a sheet metal screw through the drooping mount into the body on the fireplace or drill a screw through a C or L bracket to the side to prop it up.
12. Reinstall the LED strip.
13. Before reinstalling the hearth tray be sure to remove any media that fell inside the fireplace
14. Install the hearth tray.
15. Place the fireplace media back on top of the hearth tray.
16. Re-install the front glass.
17. Install retaining bar.
18. Please contact Technical Support at 781-324-8383 Option 3 or e-mail service@europeanhome.com for further assistance.