The transmitter usually runs up to 112 days, then dexcom app or receiver will consider it done. (But xDrip keeps reading).
To RESET the transmitter internal transmitter days counter, you can use xDrip reset command (engineering mode) on android phone. (Using RESET instead of restart helps to not confuse with sensor restart.) XDrip reset updates the transmitter day count on the transmitter, so once complete, standard dexcom receiver/app thinks it is new.
Can also be done from Spike app on iPhone. But still unconfirmed if newer transmitters allow this.
I was successful on reset transmitter starting with 80xx, using xDrip. Soon will try with newer xDrip version and 81xx trans.
Here is another discussion.
https://forum.fudiabetes.org/t/tips-on-resetting-transmittor-on-g6-via-android-phone/