Go to Keychain, select login, My Certificates search for your certificate. The name of your certificate if the first letter of your first name and full last name. In the example the name is Bill Bourcher so the search is for Boucher
Click the arrow by the name to expose the private key. Double click on the private key to display. Click on the + sign to add the Google Chrome app
New prompt will open and select Google Chrome app and select add. Once Google Chrome app is added, press Save Changes.
Go to https://client.blacksandsecurity.com and you will be asked for a password. Enter your Mac password and select Always use.