First backup all the files under /etc/yum.repos.d/
mkdir /etc/yum.repos.d/bak mv /etc/yum.repos.d/*.repo /etc/yum.repos.d/bak
Then download the repo file according to the system version and put it in /etc/yum.repos.d/
Run the following command to update the package cache
yum clean all yum makecache