Merging Level,Project with different one?

Hello, I ran into a problem. How can I successfully merge my project (where is my main menu) with one testing level in it, to a different project with a lot of levels, where is my main “workspace-project”.

Tried to move it directly in Documents to Content folder - Content stuff without success.

Not only to migrate assets (it’s easy to migrate assets), but project as a whole, e.g. Matinees, assets, blueprints, widgets, lights, etc. with one level to different project with bunch of levels.

I know that between levels I can easily open level, highlight lights, assets, postvolume, etc. and just CTRL C and V to different level. But how to do this with projects?

Thanks for fast reply!

Best Regards, Peter