Sometimes you have legacy material in another account and want to consolidate it.
If you have two macOS accounts on a single machine and want to merge them into one, macOS doesn’t offer a simple way to carry this out, but it’s nevertheless not very difficult. While you can mess around with file and folder permissions, my suggestion is to kill multiple birds with one stone by archiving and deleting the unwanted account.
Before migrating
Confirm there’s nothing in the old account you need to access from there to export.
Contacts, reminders, calendars, notes, and Safari bookmarks. These five kinds of data can be tricky to deal with if iCloud sync is off in the macOS account you’re getting rid of, and you have just the raw data available in your consolidated macOS account. Instead, follow the directions in this article about deleting your Apple ID, as the instructions are identical for ensuring you’ve exported data.
Mail. Again, it’s easier to export local mailboxes than to extract them from migrated data.
Data stored within apps. For non-Apple apps, make sure you don’t have data stored in such a way that you can’t access it by launching the app and opening a database, macOS package file, or similar item in your consolidated account.
Read more at MacWorld.com