drain oil as c123 has described.
If there is any air blockage installed. check it if it can work fine for time to come otherwise replace it with same one.
after that open (free up) the bolt on "T" attached in between CNG regulator and Air intake entry point.
Now accelerate your car at a constant high RPM and tight up the main screw on T. u will fine out a point where engine starts to crumple because of reduced gas flow. Adjust the position as per your prefernece. (ensure optimum flow of gas)
after that adjust idling (no tool needed in case of landi ranzo)
adjust as per you liking.
This is CNG tuning, plugs and air cleaner inspection is mandatory in any tuning also Distributor point (if any)
u r done