1/ Check your airfilter and housing for obstructions. If the air filter is visibly dirty, vacuum it clean or try replacing it
2/ Have your tech (the guy who installed the kit for you) check the air/fuel mixture settings
3/ Have your tech check to see if your gas regulator is choking off the delivery of the cng
By the way, it is ordinary practice among cng kit installers (in Lahore at least) to give their customers lifetime adjustment services for free. Therefore there shouldn't be any hesitation on your part or theirs to do any necessary adjustments or minor repairs. Keep in mind that the parts should also have a "desi" warranty (roughly translated to you reminding the business owner: "ap ka kaam, ap ki zabaan, ap ka naam, ap hi ki zimehwari, ham nay to ap par bharosa kiya or lagwa liya, ab ap hamaray kit ka maslah theek keejeeay"). Since competition is cutthroat nowadays, they should avoid any chance of you spreading a bad opinion of their business; by correcting the problem ASAP.
In case this is a factory installation, treat it like a warranty issue and hold your thumb to the jugular vein of the service dept mgr until your car is fixed, or he passes out (then repeat this maneuver with his successor).
Good luck, let us know how you manage.