Try this: How to Un-invite a Client in Intuit Link

To make inactive as Skylane mentioned: 
1. Login to Link and click the Gear icon on the top right corner.
2. Click on Manage Clients.
3. Find the client you wish to mark as inactive and click Mark as Inactive.
4. Close the tab and return the Intuit Link client list and press F5 to refresh the screen.  The clients that were made inactive will no longer appear on the regular Intuit  Link client list.
Hope this help!