It's really straight forward... Not.
In the top right you'll see the icon highlighted below, click on it...
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This will open a panel, at the bottom click on 'View Account Menu' to see 2 options, 'Ticketing' and 'Account Management'. Click on 'Account Management'...
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Select 'Network', there is an 'Add Members' button to bring up the following screen...
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Using the scrollbar, scroll down the window and you can search for a member to add.
It is a bloody mess, but that should get you there.