For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/devel:Factory:git-workflow:staging:ateixeira:gamescope:7/openSUSE_Tumbleweed/devel:Factory:git-workflow:staging:ateixeira:gamescope:7.repo
zypper refresh
zypper install gamescope
For openSUSE Slowroll run the following as root:
zypper addrepo https://download.opensuse.org/repositories/devel:Factory:git-workflow:staging:ateixeira:gamescope:7/openSUSE_Slowroll/devel:Factory:git-workflow:staging:ateixeira:gamescope:7.repo
zypper refresh
zypper install gamescope