I know it's posted somewhere but I can't find it
I used a 10 turn 1k trimmer pot in series with the ground wire going to the throttle. I cut the black wire and connected the ends to the resistor. Be sure to put the wheel off the ground when you first turn on the controller as the motor might start running.
With the controller on, you adjust the trimmer pot until the motor starts to move, then back off until it just stops. It's a good idea to back it off a tiny bit more just so variations in temperature don't cause the motor to start creeping at stop.
Tape it up or use heat shrink after connecting. The trimmer can be anywhere between the throttle and controller. On mine, the final setting was around 200 ohms.