The speedometer is driven by the front wheel via a rotating cable.
The cable attaches to the front wheel on the left side of the front axle where there is a small gearbox on the axle, to the left of the front wheel.
If that gearbox is not installed correctly, the speedometer won't work and neither will the odometer,
so question #1:
Does the odometer/trip meter work but not the speedometer ?
If the odometer works, then there is nothing wrong with the speedometer cable assembly.
If neither work, then you can start by inspecting the gearbox and the cable.
The cable is a 1-part assembly, an outer sheath that does not move, and an inner cable that rotates when the front wheel rotates.
We can talk about that after you answer question #1.
scoot safely,