Merge 2 databases- HOW?

This is likely not a new question, but I canon get the search function to work.
I have 2 databases which should now I see should not have been separate. What is best way to merge them? Thanks!

Select all or a portion of the content of one database and export the content to a new folder in the Finder. Then import the content of that new folder to the second database.

Moving all items (e.g. via the contextual menu or via drag & drop) directly from one database to the other should usually be sufficient.