There are probably easier ways, but the only way I've found to change the weight loss start date (& have it remain as such) is on the www.fitbit.comsite. Go to dashboard, hover over the food tile (the one with the plate, fork, knife) and select "See More". Go to the "food plan" tile and select the arrow to the right of that tile and scroll through until you see "Plan Summary". Select "Edit Plan". Find the line that says "Your starting weight was x lbs and was set on Mon Date, Year". Select the edit link located adjacent to that line. Enter the date you want to reflect your start date. Be sure that date has a weight logged (or enter your starting weight). Click save. You may need to log out / in and synch your phone app with your Fitbit device. The unfortunate thing is that you may have to search for each step listed here. I didn't find it very intuitive but if you follow these very specific steps (exactly), it works. Hope this helps.
