Honestly use your own judgement to tighten the plug.
One other tip I can give is for not only the plug but every nut and bolt on these Chinese engines is that the torque is around 10~11 Lbs unless your manual states otherwise, Also do not hold the wrench at the very end choke up as close to the head of the wrench as you can it reduces mistakes of over tightening by making it harder to screw up, You can still overtighten this way but it makes you focus more on what your doing, If you start getting scared you know you are close
