B1G IPTV can mean different things depending on the search. Some users mean B1G Player, while others mean a subscription service they want to load into that player.
What to check first
B1G Player is an interface. It does not provide channels by itself. You still need valid account or playlist details from an authorised source.
Practical Firestick advice
Before using any code or app download route, verify the destination, check the app name carefully and make sure it suits your Firestick model.
Use IPTV apps and playlists only with sources you are authorised to access. A player app does not provide channels by itself.