According to the Teltonika wiki, the configuration menu is in the Management tab. You can use it to upload backup files or configure your device that is registered on your RMS profile.
To configure your device, go to the web page for RMS. In the left panel, click on "Management" and then go to "Devices." In the Devices submenu, select "Configuration" and then "Configure Device."
Depending on the device you're trying to configure, you'll see the configuration options. Select your device and choose the settings you wish to configure. Fill in the information and then click on "Save." You will see the configuration process in the next window.
Finally, click on the "Close" button. Close the window and wait for your device to load the new settings. It could take a while for the configuration to redownload. If you have any queries, contact Teltonika support.