I had similar problems when I wanted to deploy devices with newest software available.
I had to do a research on community.teltonika.lt and have found that there is a tool called modem_updater with which you can flash the modem firmware.
Just do:
-
opkg update -
opkg install modem_updater -
opkg install sshfs -
modem_updater -g -
Select version which you want to install
modem_updater -v MODEM_VERSION_FROM_LIST
Looks like they pulling firmware from the server and mounting firmware folder with SSHFS. I was able to pull server address from modem_updater script - modemfota.teltonika-networks.com
Also followed the script logic and found exact location where firmware are stored for TRB5. You can download newest module firmware for the RG501QEU from there: https://modemfota.teltonika-networks.com/TRB1/EC25EUGAR06A09M4G_01.200.01.200
It should allow to upload it using webUI.