This may work. Works for my Axis which is made by hisun just like the Massimo.
Begin with the machine off.
Cycle the key on and off 5 times within 5 -10 seconds. Making sure the fuel pump kicks on each time.
After the 5th key off. Wait 30 seconds then start. Should be reset.
On the massimo msu500 , Start the motor, then press on the gas all the way and let the riv limiter cycle holding the gas pedal all the way down, turn off the ignition, then let up on the gas pedal. Then it should be reset.