Recently had a friend who bought a TPLINK VR1600v to extend her existing wifi , the router doesn’t have Access Point mode so you need to put this  in a double NAT setup

1. Change the router IP from 192.168.1.1 to 192.168.2.1
2. Plug the WAN port of the VR1600v into the LAN port of your existing router
3. Change Wireless Settings