Question: how to change your pokemon's ability in sword and shield?
Answer: The point of an Ability Capsule is to swap the ability of a Pokemon, and it only works on certain Pokemon who have two abilities that can be swapped. For example, Rookidee can have either Keen Eye or Unnerve, and if you don't like Keen Eye, you can use an Ability Capsule to manually swap the ability to Unnerve.