Download latest epel-release rpm from
    http://download-ib01.fedoraproject.org/pub/epel/7/x86_64/    https://download-ib01.fedoraproject.org/pub/epel/7/x86_64/Packages/p/pigz-2.3.4-1.el7.x86_64.rpm
    
    Install epel-release rpm:
    # rpm -Uvh epel-release*rpm
    
    Install pigz rpm package:
    # yum install pigz

 

REF

https://centos.pkgs.org/7/epel-x86_64/pigz-2.3.4-1.el7.x86_64.rpm.html