For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/Application:ERP:GNUHealth:4.2/openSUSE_Tumbleweed/Application:ERP:GNUHealth:4.2.repo
zypper refresh
zypper install gnuhealth
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/Application:ERP:GNUHealth:4.2/15.5/Application:ERP:GNUHealth:4.2.repo
zypper refresh
zypper install gnuhealth
For 15.4 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/Application:ERP:GNUHealth:4.2/15.4/Application:ERP:GNUHealth:4.2.repo
zypper refresh
zypper install gnuhealth