Re enter starting weight

Under your reports, you will see your weight punch in's, there is a way to delete them and start over. I had to do it when fitbit messed up my weigh ins

You must use the Web version, not the mobile apps, to update your starting weight or edit previous entries.

Navigate to APPS > Tickers > Update your weight data. Enter your desired starting weight and click Save Changes. That will update the oldest date/weight in your profile.

Alternately, navigate to MY HOME > Check-in > Edit Previous Entries.
a. Enter a new value in the Starting Weight text box and click Change; or
b. Scroll down and click on the highest page number to take you to the oldest date/weight entry. Once you find your oldest date/weight entry, under Add New Entry, enter the new date/weight and click Add New Entry. That will replace the oldest date/weight with your new one.
c. If you want to keep all of your historical data, Add New Entry at least one day older than the oldest date/weight.