Ok this is easy to make happen but will require you changing some parameters in the VFD so you'll need the manual.

If you can find the VFD manual I can describe how to do it. What you want to know is the Parmeter number for External frequency control for the Speed control. Also parameter for ON/OFF so can set to External control.
On the Huanyang VFD's which this looks like but Isn't then it's parameter 01 & 02