The Soothe Bell is a useful item in Pokémon Sword and Shield. It helps increase the level of friendliness between the player and the Pokémon holding it. You can use it to speed up the process of evolving a Pokémon whose evolution is dependent on reaching a certain happiness level.
First, you need to go to the city of Hammerlocke. You can either Fly there if you have visited it already, or you can enter the city through its main entrance. You’re going to need the Grass, Water, and Fire badges to gain access to it. If you enter through the main entrance from the Wild Area, you’ll find a Pokémon Center to the left of the entrance. You want to go to the building on the right.
Enter this house, and you’ll find three people and a Chewtle inside. Talk to the girl at the back by the fireplace, who is standing next to the Chewtle. She will briefly speak with you about how you and your Pokémon have great potential to be friends before handing over the Soothe Bell. The Soothe Bell will go in the Other Items pocket of your Bag.
To use the item’s friendliness-raising effect, you’ll have to make sure that the Pokémon that you want to make more friendly toward you is actually holding the Soothe Bell.