The Choice Band is a useful item for your Pokémon Sword Pokémon and Shield. When a Pokémon holds it, its attack power increases dramatically. However, just like the chosen scarf, it restricts them to using the first move they make during a fight. So if you have an Obstagoon in possession of the item and they use Slam as their first move, they can only use that attack for the rest of the battle. It resets after each fight.
It is important to note that this item cannot be recovered until you get the Rotom Bicycle upgrade where you can cross the water on the bike. If you don't have it yet, you must defeat the sixth gym leader and proceed through Route 9.
To find this item, you must return to Route 2, where you started your Pokémon Sword and Shield journey. Make your way through the path and proceed to the front of Professor Magnolia's house, where there is a bridge leading home from the path.
Proceed to the right side of the bridge on the side of the teacher's house. Make sure you are on your Rotom bike and proceed to the right side of the bridge into the river. Continue along the right side and it shouldn't take too long to reach a small alcove where a Poké Ball is on the ground. Reach him on the ground and grab the ball to add the Choice Band to your collection.
You want to make sure you give it to a Pokémon that prodomally uses physical attacks, which is the explode icon you see when you see a Pokémon move's category. The alternative you don't want to have is the circle with multiple rings inside it icon, which stands for special attacks.