For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:ChristianMauderer:opensuse-installations:freecol/openSUSE_Tumbleweed/home:ChristianMauderer:opensuse-installations:freecol.repo
zypper refresh
zypper install freecol
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:ChristianMauderer:opensuse-installations:freecol/15.5/home:ChristianMauderer:opensuse-installations:freecol.repo
zypper refresh
zypper install freecol
For 15.4 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:ChristianMauderer:opensuse-installations:freecol/15.4/home:ChristianMauderer:opensuse-installations:freecol.repo
zypper refresh
zypper install freecol