iMac OS is at initial state on power on - no way to communicate with computer

Just acquired a wiped and refreshed corporate A1419 27" iMac late 2013. The software (OS) shows only initial screen (country pull down list) at power on. I want to add new wireless keyboard, separate purchase and (unpaired).

How do I "bootstrap" this so I can initiate bluetooth and pair the mouse and keyboard.

I was told the OS is the latest that the Late 2013 iMac would support. But I can't get to anything else until I'm able to initiate the OS.