Before exporting your level, you need a thumbnail of the level to do that:
WASD – move around
Q – up and Z – down
Click the Unity play button
Press F9 to take the screenshot or press F8 to enter freeroam camera mode.
Once in the free-roam camera the following shortcuts are enabled to control the camera:WASD – move around
Q – up and Z – down
Mouselook – look around
Mousewheel – change FOV
Mousewheel – change FOV
F9 to take the screenshot
Now go to Human -> Human Export