To connect your Fitbit to your Healthbank profile go to your personal Dashboard and click on the "Connect your device" button.
Once you have clicked on the "Connect your device" button you will be redirected to the Fitbit login page. Choose to login with "facebook" or your "Google" account or use your Fitbit login details and click on "Login".
Once you have logged on to your Fitbit account, Fitbit will ask what data you would like to share with Healthbank. After selecting the data you would like to share click on the "Allow" Button.
You will then be redirected to your personal Healthbank Dashboard and you can now see "Your Health Snapshot" with your Fitbit Data.
This is how you can connect your Fitbit to Healthbank!
I hope this helped!