Hi where is the FIT file?
Either on the watch, or you can export it from the activity page on Garmin Connect Web (use the export option Original Format to get the FIT file). Just please note, that the FIT file is in a binary format, and you won't be able to read anything from it without a special app, like for example the Fit File Repair Tool. Anyway, I am not at all certain that the FIT file contains the number of steps, I am rather sceptical about it.
Another way to get the number of steps of any of your activities is simply having a look at the daily Steps graph on Garmin Connect Web » Activities » Steps, zooming into the part of the activity (select the part with the mouse), and then reading the steps numbers before and after the activity in the mouse-over tooltip, while you are hodling the mouse cursor over the start and the end of the activity.
The only inconvenience is, that the steps are shown only with the frequency of 15 minutes, so you may not get the values exactly for the moment the activity started or ended. However, since you usually move less before and after the activity, than during it, it should not be a big problem.