how can I manually add a lead to a journey?

how can I manually add a lead to a journey?

Anyone has an idea how to manually (!) add a lead to a journey? I have a couple of journeys up and running but now I would like to add a single not-so-new lead to a a new customers' journey.

How can I do that?

I did not find any solution so far, neither from the "manage leads" list nor in the journey menu.