Of course, if you've been using your Band 2 all this time, without a reset, then you're fine already. But most of us will have sadly let the battery run out by now, in which case it's time to somehow activate it again. There are some Android options, but that's perhaps an article for another day. In the meantime, keeping things Windows-only...
From the Unlocker page:
What do I need?
Here's the list of what you'll need:
A Microsoft Band 2
The standard USB cable
A Windows PC (Only tested on Windows 10, older systems might work)
.NET Framework 4.8 Runtime (Probably already installed)
Will this bring back all functionality of the band?
Not quite. You will be able to use the device like you did back in the days, but there are some restrictions.
Everything that needs the app on your phone won't work. This includes weather, sync, mail, calendar, notifications ...
Also, the app usually downloads an ephemeris file from the Microsoft servers to help with GPS acquisition. Since the servers are shut down and I don't have a reference file there is no way I can make this work. GPS WILL work but it WILL take ages (1-5 minutes usually) until you have a lock.
Do follow through and read the full instructions if you're interested. Comments welcome on how you get on!
PS. Personally, I've tried all the wearables and bands and I struggle with something permanently on my wrist, cool though it often is. Which is odd, as I used to wear a watch all day back in the 1980s and 1990s before smartphones were invented!