Question about the functional principle unloading process Mercedes Actros 3344 with tipping trailer

Hello guys, Have a question to better clarify an accident. What must be activated/ deactivated in a Mercedes-Benz Actros 3344 with tipping trailer to tilt the trailer? Is it the case that the parking brake has to be tightened to lift the trailer’s loading area? And where is the tipping process triggered? On the trailer? or in the cab? I’m now interested in knowing if it’s possible to pre-roll the truck when sand is unloaded by trailer. If yes? How far is it? can the Fahzeuh preroll? Thank you very much for your help =)