Extra Packages for Enterprise Linux (EPEL) is the group that creates, maintains and manages high quality packages for RHEL, CentOS and Scientific Linux.
To enable the repo all that is needed is the epel-release RPM.
yum install https://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm
yum install https://dl.fedoraproject.org/pub/epel/epel-release-latest-8.noarch.rpm
The epel-release RPM will setup the RPM EPEL gpg key and the required yum