For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:Bumblebee-Project:nVidia:390.157.2/openSUSE_Tumbleweed/home:Bumblebee-Project:nVidia:390.157.2.repo
zypper refresh
zypper install dkms-nvidia
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:Bumblebee-Project:nVidia:390.157.2/15.6/home:Bumblebee-Project:nVidia:390.157.2.repo
zypper refresh
zypper install dkms-nvidia
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:Bumblebee-Project:nVidia:390.157.2/15.5/home:Bumblebee-Project:nVidia:390.157.2.repo
zypper refresh
zypper install dkms-nvidia