Referenceing multiple soltuion from Git

Hi All,

I published a class A in a Github repository. In parallel I built a soltuion B (which I leverage a private Git repostory for).

Now I would like to reference class C in soltuion B but am compeltely lost. When I use local files I can "Add Existing Item" and reference the file but with git this does not work anymore. How do I solve this?

Thank you

Roger