Connecting extender to new WiFi router/network

I recently upgraded my router with virgin, which means I have a new WiFi network and password. When I pair the Netgear extender to my new router, it doesn’t find the new network, but instead, still finds the old network (which is no longer connected). I’ve pressed the factory reset button but it makes no difference. Can anyone help? Tried to contact support on here but can’t find a number and the website just keeps sending me in circles! 😡