Once you create the team, you can add workspace members to it.
Navigate to the Teams menu in Manage account.
Search for a team in the search box.
Click the Pencil icon to edit the team and add members.
Click "Add team member"
Select the member from the list.
Select their team permissions level.
Then, click 'add team member"
The member is added to the Team.
They will not be notified, but they will instantly have access to all content that was previously shared with that Team.
To add someone to a Team, they must be a member of the workspace.