This is more so I can remember, but it’s basically 3 steps.
Apply all the latest patches to your Centos 8 systems
dnf update -y
reboot
Then install the Centos 8 stream repo’s
dnf install -y centos-release-stream
Then swap from Centos Linux repo’s to Centos stream repo’s
dnf swap -y centos-{linux,stream}-repos
Then do a distro sync to get everything back in sync
dnf distro-sync -y
reboot
You should be golden at this point