Using an RBR50 as extender router plugged into a RBS50

[jafisto]

I have two buildings. I am trying to have one ISP. 
I have an ORBI mesh system in building 1. I also have an RBS50Y on the outside of building 1. 30 feet away I have a direct path to a window in building 2, where I have a RBS50. This is getting good internet on that level of the building, but I need internet in my basement and I have a RBR50 sitting around. I can run an ethernet cable to it from the RBS50 upstairs. I want the RBR50 downstairs to function as an extender with the same name and password. 
When I try to set up the basement RBR50, it acts like it is the first router back in building 1 (same login to the router and all the same info) and I can't change the name and password. 
How can I change the name and password on this basement RBR50?

[FURRYe38]

Only configuration that could work in set the RBR50 to AP mode with a different SSID name and use far apart channels from the main RBR.