Good day. Thank you for your detailed explanation of the question.
There are several ways to update the firmware but from what I can see, the device is at hand, which means an OTA update would not be necessary. You may either use the Configurator (in this case, the device uses an older FW which isn't supported by the newer Configurator) or a Firmware Updater. Therefore, I would suggest going with the latter, as it will be more suitable for your case.
To receive firmware files, updater, and documentation on devices, please contact your sales manager/distributor as we do not share firmware files/updater and other files in the community forum. If you don't have any contacts with our Sales managers, please contact them on our official website https://teltonika-gps.com/
and click on the "Contact Us" icon. When you will click, please fill out the form and submit it.
Note: as a topic, please choose "Vehicle telematics" or you can send an e-mail with the description of your situation to firstname.lastname@example.org
Thank you for your understanding.