To unregister the computer a file has to be removed. Login as root user and execute the following command
mv /etc/sysconfig/rhn/systemid /etc/sysconfig/rhn/systemid.backup
Now fix base repositories by reinstalling
centos-release package.
1. Check what version you are on:
cat /etc/redhat-release
CentOS Linux release 7.5.1804 (Core)
2. Remove centos-release without dependencies:
rpm -e centos-release --nodeps
3. Install the
centos-release package for your release
rpm -Uvh http://vault.centos.org/7.5.1804/os/x86_64/Packages/centos-release-7-5.1804.el7.centos.x86_64.rpm