Wall mounted electric fireplaces are commonly installed straight onto a wall using screws and so all that there is to do is unscrew the screws for the fireplace to come away from the wall.
We used a standard screwdriver to install our fireplace and so we’d use the same again to remove it from the wall.
These electric fireplaces can be heavy appliances and so it’s best to have one or two other people holding the fireplace while you remove the screws.
With the screws removed, a wall mount fireplace will typically come away from the wall.