Invitations can only be resent through the Administrator tool by using the following steps:

1. Log into the Admin Tool 
2. Left Click on the Users node in the TreeView Pane
3. Locate the specific user in the content pane on the right
4. Right Click on the user's name (or hold down the ctrl/shift keys to select multiple users at the same time). 
5. Choose “Invite to Privia…” from the context menu to send out new invitations.