This app was mentioned in 2 comments, with an average of 2.00 upvotes
You need root, an older Fitbit app (ver 2.10.1) and Tasker.
http://tasker.wikidot.com/notifications-to-fitbit-charge-hr
or Xposed and the app, SmarterBit (not sure if it still works with the newest app)
https://play.google.com/store/apps/details?id=com.mikerinehart.smarterbit
I believe the other app was called SmarterBit. https://play.google.com/store/apps/details?id=com.mikerinehart.smarterbit