Are you able to provide us a screenshot of the settings of your old router? We need to analyze it further as we don't have any reference for third party devices.
Usually, if you are going to use an old router as an access point or extender, the configuration should be set to 'Dynamic IP address'.
Thanks for your quick response.
I've attached images of settings for old router (vivid Huawei) and settings for TPG router.
I had changed the IP address on VIviid to match TPG. I'm new to all this. I have also tried reset on the Vivid. THe vivid takes a sim card BTW.
Thank you @mogga71.
As stated on your screenshot (11) post, after you've applied the Dynamic IP settings on it, the TP-Link modem that we've provided should be connected to the WAN/LAN of your Vivid Huawei router via Ethernet cable.
Once connected, try if you are able to access the internet using the WiFi of your Huawei router.
Update us if it's working or not.