If you have a contact list stored in your legacy domain, you can easily import these into your new Google Workspace account.
On the Contacts home page, look in the top right corner for the import icon
Select the file stored on your desktop
Import
If you uploaded any external contacts to your Contact list, you can always go back and make edits.
Hover over the contacts name in contacts.google.com
Click the pencil icon to edit
Save once changes are complete
Please note: All organizational contacts are synced automatically so you cannot update these