How can i Find the error

i am maintaing honda civic and installed a gas kit too.Now my car works on both but from few days i am facing problem that while i am traveling on gas it switches to petrol and when i travel on petrol it switches to gas(automatically)

i have taken my car to petrol,Gas specialists and even changed the switch too.but problem exist.what to do next??

Since you installed some sort of kit, (?) go back through the instructions again, step by step, and maybe you’ll pick up the step you missed that will fix your issue. Sit down and read slowly, just you and the instruction manual.
Especially if there are variables in the instructions such as “if you have one of these do this, if you have one of those do that”. Engine size, year model, etc are all variables that need read through carefuly.
Are you using the right kind of gas the kit is made for ? CNG, Compressed natural gas ? propane ? LPG, Liquefied petroleum gas ?
Does the manual show a tech help line to call?

Here in the U.S., where the forum is based, we typically use “gas” to refer to gasoline (your “petrol”) and use initials for other fuel types. Without knowing what type of “gas” you’re referring to or what “kit” you installed, it’s a tough puzzle.

I agree with Ken’s points, particularly about going back over the installation instructions.

Perhaps you need replace the automatic switch with something manual.