If you search for “install kontact centos7”, you find the first link: https://www.kolabsys.com/installation-guide/kontact-centos.html
Unfortunately, that does not work. Even if you add the Kolab 16 repository (wget https://obs.kolabsys.com/repositories/Kolab:/16/CentOS_7/Kolab:16.repo) so that libkolab etc can be installed, you still have conflicts because kdepim-libs is installed from the base repository.
It seems, that the packages on OBS are targetted mainly for Ubuntu: https://obs.kolabsys.com/project/monitor/Kontact:4.13
Then I looked if Kontact is available in Epel, but it is only available for Fedora: https://apps.fedoraproject.org/packages/kontact
Then I found the copr of Rex Dieter, which provides uptodate packages for Kontact and is maintained by the Fedora KDE-SIG: https://copr.fedorainfracloud.org/coprs/rdieter/kde4/
So to install Kontact on CentOS7, you need to do this:
cd /etc/yum/repos.d wget https://copr.fedorainfracloud.org/coprs/rdieter/kde4/repo/epel-7/rdieter-kde4-epel-7.repo yum install kontact