There is no official guide to migrate from Rocky Linux to CentOS Stream, however, it can be achieved by using official CentOS to CentOS Stream migration guide

  1. Install centos-release-stream package
dnf install https://vault.centos.org/centos/8/extras/x86_64/os/Packages/centos-release-stream-8.1-1.1911.0.7.el8.x86_64.rpm
  1. The next step is to swap Rocky Linux repositories to CentOS Stream ones. This is done with dnf swap centos-{linux,stream}-repos -y command. However, this command will cause multiple conflicts in Rocky Linux. To solve them:
  • copy /etc/pki/rpm-gpg/RPM-GPG-KEY-centosofficial file from any Centos Stream system into Rocky Linux
  • remove conflicting packages: 
    rpm -e --nodeps rocky-repos
rpm -e --nodeps rocky-release
  • complete installing CentOS Stream repositories 
    dnf swap centos-{linux,stream}-repos -y
  1. Switch to CentOS Stream
dnf distro-sync -y
  1. Verify installation and reboot the server:
cat /etc/centos-release
reboot