Hi @nguyenvq ,
Welcome to the community!
TPG customised the firmware of the supplied TP-Link Archer VR1600v modem/router for security purposes this caused the modem's back up configuration no longer available.
You may visit this thread for additional reference: How to back up settings in the Archer VR1600v
Let us know should you require further assistance.
The TPG supplied modem, TP Link VR1600v does not support the backup and restore function.
If you want to restore the original firmware of the modem, you can check TP Link's website or contact TP Link directly for assistance.