Unfortunately, there is no way to reset any G6 transmitter with a letter in the second position. Sensors can be restarted, but not newer transmitters.
Depending on your software, though, you can get extra life out of it. Dexcom software won’t let you start any sensor with a transmitter more than 90 days, old. You’ll get 91-99 days life max if you use the Dexcom transmitter and/or app. If you use the T:slim X2 pump as your primary receiver, it relies solely on battery life, not a set number of days. There are theories that you can’t start a new sensor after either 100 or 110 days on the X2, but I haven’t seen that verified anywhere. 3rd party connection apps, like Xdrip, don’t have a hard stop at all. They’ll keep collecting data until the transmitter dies.
Unfortunately, once the battery dies though, there’s currently no method to successfully replace it and reset the software. I actually tried with an 8G before I knew the “firefly” sensors were different. They use different batteries in them. I couldn’t even get the battery out, despite successfully removing the plastic housing. The battery is cased in something approaching tin foil that disintegrates under the lightest touch. You can’t pry it free from it’s soldering.