EX6250 Extender - Unplugged, now cannot set back up, cannot remember original user name and password

Hello, and thank you.  I did this - sort of - already.  I used a PC, as I have no laptop.  But I could not connect an ethernet cable directly from the extender to the PC - I had to hook it up to the router, which is connected to the PC - because my PC has only one opening/plugin for an ethernet cable.  And the PC has no 'wifi'; it is connected directly via ethernet cable to the plug in my wall.  If I disconnect the PC's internet cable in order to plug in the extender directly to the PC, then I will have no internet in order to go to the website you referenced. 

I did try this sequence with the extender plugged in and connected to the router via ethernet cable (after I had reset it to factory settings)/connected to the PC, but the website you referenced said I was not connected to 'wifi', which of course I could not be, since the PC is not on wifi - it generates the wifi (right?)...IF I'm understanding this correctly...which I may not be!  If I disconnect the PC's ethernet cable from the plug in the wall and plug it into the extender directly, then I will have no internet, correct?  I did try to reference that website with a device connected to wifi - my iPhone - but the website again said I was not connected to wifi.  See why I'm tearing my hair out?  I think I may be missing something essential here, but don't know what it is.  Sigh.  Just an FYI - I don't have cable/DSL/satellite internet; instead, I have radio wave internet.  The plug in the wall that the ethernet cable is plugged into is connected to an antenna on my roof, which communicates with some type of tower a few miles or so away.