Configuring a single login for multiple accounts
If your organisation has a management environment (previously overview account), you can also grant a user of a sub-account access to other accounts. This person can then log in to each of those accounts using the same login and password, without gaining access to the management environment itself.
You can configure this in the user management of the management environment, not within the account itself. What the user is allowed to do within such an account can be managed using the permissions and roles in that account. Read more about this difference under user management at two levels.
Giving a user access to multiple accounts
Open the user management for the account
In your management environment, go to the account the user already works in and click the number of users next to that account name. You will now see everyone who has access to this account with their own login.
If someone does need access to the management environment, and therefore to all accounts, you can create an extra user for the management environment.