If you did not sign in with facebook during the set up process you can go to the settings and link to it.
Go to your profile.
Click on the gear icon to get to settings.
Click on "Profile" link.
Click on "Account" link.
Click on "Facebook account linked"
It will redirect to Facebook where you will need to agree to let the Hidrate Spark app link to it.
A check mark will appear when it has sucessfully linked.