Hello,
Firstly, from the screenshots, it seems that you have legacy firmware installed. If possible, I would strongly recommend to update the device to the latest firmware version with 'keep settings’ option turned off. This will erase your current configurations, but will ensure that there are no migration issues, since the differences between your current firmware and the latest firmware are substantial. Firmware for RUT955 can be downloaded from here.
Then, to send GPS coordinates via MQTT, you can use Modbus monitoring to read GPS coordinates from RUT955 itself, and then send it to your MQTT broker using Data to Server functionality.
Please, take a look at this forum post here which shows an example.
Kind Regards,