If your train is stopped, put the throttle and AFB levers to 0 / Off, reverser forward (you need to do this before you turn AFB on). If your train is moving, throttle to 0, AFB lever to MAX. After that, what you need to do to turn AFB on changes depending on the train you are driving: The ICE3 has some control to do it in the MFD. I can't remember exactly how without seeing it in the game, and I can't right now For everything else, the switch to turn AFB on is usually located under the control desk, on the left side. You might need to stand up and crouch to see it. It is usually a round turn left/right switch. The exact location might vary because the cabs of different trains are not the same. After you find the AFB switch and turn it on, you can use the AFB lever to choose the speed. Don't forget to move the throttle lever to something other than 0 too. PS: Talent 2 uses Tempomat instead of AFB -> Just press the Tempomat button to the left of the throttle lever while the train is moving, then use the tempomat lever on top of the throttle to adjust the speed.