You should be able to print out a parameter manual for the VFD from the internet, If you use a potentiometer to control the speed of the motor you need to select that option for the VFD.
Most VFD's out of the box are set up to be controlled by the keypad, you must change one of the parameters to allow the VFD to be controlled externally with an input like the potentiometer or a variable input signal like a 4-20ma or a 0-10VDC signal generated by a DSC or PLC system. You will have a large number of parameters to choose from in controlling the VFD most of them will not be needed for your application. You usually need to select the motor values, the voltage, the frequency, ramp up speeds, braking speeds, E-Stops, Interlock safeties, etc. If your existing VFD has a digital display, you can usually scroll through the parameter settings and write them down one at a time. Most of them will be the default setting, the settings that are different from the default settings will be the ones you want to pay attention to. If your VFD does not have a display you would have to use a computer with a software program and cable to plug into the VFD to copy the program or change the program or upload a program.