Ensure you're on the latest CU of Server 2012R2
Remove/Reinstall WSUS
https://www.ajtek.ca/wsus/how-to-remove-wsus-completely-and-reinstall-it/
Once it's installed follow my guide
https://www.ajtek.ca/wsus/how-to-setup-manage-and-maintain-wsus-part-1-choosing-your-server-os/
It will get you going.