It is likely the float valve is not seating properly. Needs cleaning or replacement.
By calling a licensed master plumber / licensed gas fitter / Gas supplier
You can stop a leaking gas tank, by making a paste of soap on the hole of the gas tank.
Take it to a trained technician
If it is leaking at a fitting, it is either a bad flare or it isn't tight enough. Gas or flare fittings should be put together dry, Do no use pipe dope because this can cause a leak between the...