Make sure that you joined the session in Google Chrome. If you are either a moderator or presenter in a Blackboard Collaborate session, you will have the ability to share out your Desktop.
Open the Collaboration Panel.

Click the “Share Content” button.
Click “Share Application/Screen”.
Select “Entire Screen”.

Click “Add to Chrome”.

Click “Add to Chrome”.
Click “Add extension”.
Click the x in the upper right hand corner of pop-out window.
Close the Desktop Sharing – Chrome Web Store tab in your Google Chrome browser.

Now you will see the below message.
Reload the session by refreshing your browser.
Click on “Share”.
Click on the (+) plus sign to add a new tab within your Google Chrome browser. This will solve the tunnel vision.
Everyone who are currently in the Blackboard Collaborate session see your screen.