Plumbing and Piping - best way t o fix a small gas leak

I have a small gas leak on the ng line that goes into my furnace. I have located exactly where it is. It is at the connection between a length of pipe and an inline shutoff valve. The leak seems pretty small, I can just barely smell gas but only when I try to smell the pipe up close. The leak was found when a local contractor came out to do a home energy audit and used a tool to check along the gas line for leaks.

What is the suggested fix is this something I can fix myself?

Two choices, replace the fitting and seal the threads with either Rectorseal (a pipe dope for gas lines) or Yellow Teflon Tape (yellow for gas fittings).