Chromebook App Help

My computer took a dive a while back and I ended up getting a chormebook. I don't use my computer for much at home other than photos and internet so it's worked well for me up to this point. I got a fitbit from a friend and I tried to do the start up but got a message saying that the file wasn't supported and that I needed to download a chromebook app that would open it. However, the message didn't tell me what app to download. I am pretty much computer stupid so if anyone could suggest an app that I could use and where I would get it from I would appreciate the help!