It's not a silly question, but rather one that invites some investigation.
In general, an AC motor spins at a speed determined by the frequency of the 3-phase power supplied to it, based on its number of poles and construction.
Are you troubleshooting a system that is not producing the motor shaft speed that you expect it to, like a conveyor that speeds up or slows down ?
Or are you trying to "trim" the motor speed based on a control loop or feature other than the Command Frequency that the drive gets from its keypad, analog input, preset, or PLC network connection ?
The more context and detail you can provide, the better !