The Package Manager CLI commands that require authentication, push and yank, are broken in the current Rhino 7 WIP (7.0.20126.10465, Tuesday 5th May 2020). If you need them before next Tuesday, please use the daily build below.
http://files.mcneel.com/dujour/exe/20200507/rhino_en-us_7.0.20128.05305.exe
Sorry for the inconvenience!