@John-Langfield As Nick told you, the speed is set by the map owners, you can't change it but...

what you can do is make a tour, take note of the time that the map calculates, then get out on the lower speed scooter and see how long you do over that route. Afetr some attemtps you may find an easy multiplication factor to calculate the real time it takes you.

But this will only be a guideline (as are also the time calculations from the maps, as no-one can really predict how fast an individual would ride