I do see slot 2 populated with no information
Then the operating system will not change this. No, the OS does not need reinstalled. In the days of NT the hall.dll needed to be replaced with a multi-processor DLL, but no more. You can add the processor or processors. When you restart the computer, Plug and Play detects and installs the processor or processors. I'd contact dell support or try asking for help in dell forums for problems with the hardware.
https://www.dell.com/community/PowerEdge-Hardware-General/bd-p/PowerEdge-General-HW
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