the first step, moving the submissions to the other journal, could probably be achieved with an SQL-UPDATE-query in the database. You would have to change the "journal_id" field in the "articles"-table and probably also the "journal_id" field in the "issues"-tabel (this will be required, if your journal has already assigned articles/submissions to issues). A database query however would only be a suitable way, if you find a way to write a select statement, that uniquely identifies the articles/submissions that need to be moved. Are they all in a certain article number range? Do they have specific titles in common? Do they have certain DOIs or other public identifiers that can be used for grouping the articles that need to move?
If there is, and if you want to give it a try moving the submissions with a database query, I strongly recommend you to try this on a non-productive system first. You could copy your OJS installation to a local computer first, try the sql query and see if it works or if there's some dependency that has been overlooked. If you made sure that it works, you can also run the query on your public OJS's database server.
I don't know of any way for editors to move submissions between journals, but there seems to be some demand around this thing. You can search this forum for other similar request and maybe second this as a feature request somewhere.