Being one of MTroniks newer speedo's it may well have the one touch setup. Simply press the SET button within the first couple of seconds of turning it on (while the LED's are flashing) , then move your transmitter from neutral to full throttle, hold it there for half a second then back to neutral, then full brakes and release the throttle.
That should be it, no more buttons to press
Leave it too long after the leds start flashing and they'll start flashing slightly differently, and pressing SET now will take you into the programming mode. Not sure what the options are here, but it includes selectable frequency.