When swapping routers, it's essential to have your TalkTalk broadband username and password ready. These credentials would have been provided when you initially set up your service. If you do not have them readily available, you can retrieve them from your current Sagecom Fast 5359 router's settings.
Once your TP-Link Archer VR900 is connected, log into its user interface and navigate to the Quick Setup or Internet Settings section. Select VDSL as the connection type, then enter your TalkTalk login credentials. Most settings, such as the VLAN ID, should auto-configure