Press 0 (zero), fly to a suitable location with numpad 8,4,6,2 keys. Get close to the ground and press F9. This will drop your truck and trailer (upright) at the current camera position. After flipping my truck in Euro Truck Simulator 2, I manage to set it up right again by manipulating the steering wheel and acceleration pedal. Sorry for low quality video, I had to pull La56efi.

how to flip truck in euro truck simulator 2