Click 'choose file' and find the file you got from Vitadock.
Click 'load' to load the contents of the file.
Option 2
Open the resulting csv file in a text editor — not in Excel or something like that.
Copy the contents into the input area below. You don't have to remove headers, as only lines starting with a date and time (like '02/12/2018 - 18:59') will be processed. Please check whether each line indeed starts with a date, because some lesser editors do not correctly place the newlines.
Click 'Convert into Fitbit-format'.
Either copy the resulting text from the output area below into your text editor and save the file as a csv file, for instance 'myweight.csv', or
Only import data for one year at a time in Garmin Connect. Otherwise it will throw an error.
If you have multiple measurements for one day, only the first one will be used.
I made this page for myself, but you can use it too. Completely at your own risk, though.
No files are stored on the server. I am not interested in your data.
If something doesn't work out, or you encounter any problems, check my contact info at http://www.reuneker.nl.
It seems to be the case that Garmin Connect limits the import of Fitbit data to weight, BMI and fat percentage. Any other measures, like bone or muscle mass are ignored. I cannot change this, as this involves Garmin's implementation of the import functionality. Also see this Garmin Support page.
The Vitadock, Garmin (Connect) and Fitbit are registered trademarks by their respective owners.
Updates
2019-11-20: added options for reading and saving files, so no need to open file in texts editors anymore
2019-11-19: corrected fat label, added bone mass, hydration and muscle mass