How to Control SM1 Inverter Drive Frequency with Arduino?
Based on a quick scan of the manual, it appears that the only means of remote control of the speed/frequency is by the analog input, either 0 - 10 volts or 4 - 20 mA.

I don't see any mention of RS-485 or PWM control (except that PWM may be used to generate the 0 - 10 volt/4 - 20 mA signal).

Please note that I have not used this device - I just quickly scanned the manual.  I suggest that you carefully study the manual to see how, or if, you can control it remotely.