RS700 connection to extenders

I replaced an older Netgear router with a Netgear RS700 last year and added two extenders.  The one in the barn across the street seems to function correctly but the one hardwired to my router apparently does not.  I thought it was providing wifi to those on the patio outside but now that I see how I'm exceeding my Verizon data limit, I'm guessing it's not.  

I've tried resetting it and it provides me with a Network_EXT network which functions and provides internet but I don't know how to connect it as a hardwired extender to my network.  I would think of just using it as it is but it has no associated security.

I had Netgear help setting this up but I'll admit to some confusion.  I wanted to keep the same network name but when we finished that wasn't the case - half were changed and half were not and I had to make changes on my own.

 I have an extended warranty because I suspected I might run into issues down the road.  When I've contacted them, I don't understand what they want me to do and I quickly get frustrated.  

I'm a female senior citizen but I've been using computers successfully for a long time.  I am just not comfortable setting up and revising a network.  The Nighthawk app is useful for some things but apparently not this.

Thanks for any help you can offer!

Martha