cannot connect second extender ac750 to network

Tried to connect with simple wps set up but failed.

So followed previous extender connection instructions and used ethernet cable between extender & laptop.

First effort failed part way through process - network security key not recognised.

So did a factory reset and started again. Gave extender new ssid for 2.4 & 5 Ghz band and completed setup

This time all seemed to go well but when connecting extender close  to the router to test connectivity same problem - no connection with wps? The router and wifi connection is working fine.

So did another factory reset to try again but this time no access to new extender set up gene?

Figured if I cleared everything I'd done out of memory and started again I might have some success.

Is there data that needs to be cleared out elsewhere?

Can someone advise how I get back into the gene.