How do I connect my AC 1750 Smart WiFi Router to my WN 2500 RP range extender?

[tangonovember]

I have just installed an AC 1750 Smart WiFi Router (Netgear R6400) to replace my Netgear WNDR 3400 router.

The router is directly wired into my desktop. 

I have been able to establish wireless access to my phone and tablet.

However, I have not been able to establish a connection to my Netgear WN 2500 RP range extender, so I cannot connect wirelessly to a second desktop in a remote part of the house.

[TheEther]

You can use WPS.  Log into the R6400, go to ADVANCED > WPS Wizard and click the WPS button.  Then go to the WN2500RP and push the physical WPS button on the side within 2 minutes.

Or you can push the factory reset button on the WN2500RP and set it up as a new extender.