For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:tiwai:xfce/openSUSE_Tumbleweed/home:tiwai:xfce.repo
zypper refresh
zypper install xfce4-settings
For 16.0 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:tiwai:xfce/16.0/home:tiwai:xfce.repo
zypper refresh
zypper install xfce4-settings
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:tiwai:xfce/15.6/home:tiwai:xfce.repo
zypper refresh
zypper install xfce4-settings