You will have to identify make/model of your ebike. A picture of the controller wires and the display helps too, Some ebikes have speed limiters in the display. Some have no displays and will have a speed limiter wire, Some have both a display setting and also a wire. Some have neither. If you want help, you have to give more details. There is no universal answer. When they have a wire, it's more often a power setting, not a speed limit.
Whatever you do, don't be cutting wires at random. The speed limit wire, if there is one, will be a pair of single wires of same color, with matching connector. You have to examine the whole harness til you find it.
If you get the wrong wires, you could be plugging a light output into a ground. Fries the controller. So don't be connecting wires at random either.