After adding a repo I get
localhost:~ # zypper **dist-upgrade** --allow-vendor-change --allow-downgrade --from packman
Unknown command '**dist-upgrade**'
Type 'zypper help' to get a list of global options and commands.
In case '**dist-upgrade**' is not a typo it's probably not a built-in command, but provided as a subcommand or plug-in (see 'zypper help subcommand').
In this case a specific package providing the subcommand needs to be installed first. Those packages are often named 'zypper-**dist-upgrade**' or 'zypper-**dist-upgrade**-plugin'.