We do not have a special set of commands just for BGP configuration but you could use UCI commands for that. More information about UCI commands: https://wiki.teltonika-networks.com/view/UCI_command_usage
You can use the UCI SHOW to find out the command you need to configure BGP. Run the UCI SHOW command once and copy the entire default configuration to Notepad++. Then prepare the entire BGP configuration via the Web UI and save it. Then run the UCI SHOW command again. Copy the entire configuration with changes to new Notepad++. Take advantage of the plugin provided by Notepad++, which can compare two files:
This way you will find out what UCI commands you need to insert in CLI to configure BGP.