Whilst you can perform most user administration from your own login, there are some operations that are specific to a sub-organisation and you need to do those whilst acting as the sub-organisation - examples are managing groups, resources or permission sets. This can sometimes mean a little more work, but it also provides you with the flexibility for different parts of your organisation to operate in different ways.
To impersonate a sub-organisation the best way is to go to the organisation list button in the top bar:
This will give you a list of the organisations below you, associated administrators and on each line will an impersonate button ( ):
If your organisation is very large, the page may take a little longer to load.
Once you've clicked you will see the dashboard of the impersonated organisation.
The breadcrumb just below the menu will show you as acting as this organisation until you decide to return to acting as yourself or log out.
Clicking on the home icon or the OpenAthens logo at the top of the page takes you to the dashboard of the impersonated organisation rather than your own. To return to acting as yourself, click your own username in the breadcrumb.