IIRC the Teco works on 10 Volts. The frequency input control wants 0-10 Volts to set the speed. The frequency output has 0-10 Volts depending on the speed.

Usually you get the input by wiring a potentiometer across 0-10 Volts from the inverter so depending where you turn the knob the centre pin (the wiper) has 0-10 Volts on it.

Assuming you haven't got the serial control version it has a pot on the front cover to set the frequency and you have to tell it to use the remote control. You can tell it to do most anything you want but until you get the hang of it's menu system it is a bit brain numbing.

You don't have to use a potentiometer for the frequency control, you just have to make sure your signal has a 0-10 Volt swing off the inverter ground.