Have you tried copying your project’s buses and pasting them into the new project before copying and pasting the events across?
When FMOD Studio pastes an event into a project, it checks for a bus with the same name and routing path as the bus the event was routed into in the original project, and routes the pasted event into that bus if one is present. Thus, if you copy and paste your buses across before copying and pasting your events, the routing should all be set up automatically.