Best bet for me would be to stop use of the old database...

Alternatively, you could use an append query - https://599cd.com/blog/display-article.asp?ID=1459
to transfer the records across.

Lastly, maybe link the various tables from the old database into your new table. Is this a temporary issue or permanent?

This is a one time thing.  I intend on splitting the database so that the tables reside on one drive and the others on the individual computers. In that way I won't have to do this again.

Access Online Don't use One Drive

If you have multiple people using your db you should really look at Split Your Database.

That way you could potentially be working on a development copy of the Front End and the Back End is kept intact.

That being said I never develop on a live database.  You should make a copy and develop there then when you are sure your code is working properly distribute the new Front End to your users.  Take a look at the Access Updater

What ever you do Back UP!!