The app has two methods to reconnect a v2 sensor to a Wi-Fi network. The default mode is called BlueConnect, which uses a temporary bluetooth connection to send network credentials to the sensor.
First, check that your sensor is not already connected! Press the RESET button once (short press) and watch the status LED. If you see a solid BLUE (CYAN) colour for 5-10 seconds, the unit is already connected to a Wi-Fi network.
Reconnect a sensor using BlueConnect
In the TankMate app, go to Settings > Sensor / Tank Settings > Edit Network Settings
Put the sensor into BlueConnect mode - unscrew the sensor from the tank. Turn the sender unit upside down, and hold the RESET button for 6-8 seconds then release.
The status LED will blink slowly - dark blue - when in this mode
The unit will go to sleep to conserve power after 3 mins. Click RESET again to wake it up if required.
Follow the prompts in the app to scan and connect to the sensor. Ensure the status light on the sensor is still blinking. Select the TankMate device, and proceed to the network SSID and password page
Slow blue blinking = ready to reconnect via BlueConnect