In the region where different type of gas isn't available just one kind of gas and it's unknown What should driver use to maintain fuel system of the car?

If only one type of gas is available and it's unknown, the driver should consult the vehicle's owner manual or manufacturer guidelines to determine compatibility. If the fuel type is entirely unknown, it's advisable to avoid using it until more information is obtained to prevent potential engine damage. Alternatively, using a fuel additive designed for cleaning and maintaining the fuel system may help mitigate any issues, but it's best to proceed with caution.