Source: Tasha's Cauldron of Everything

Prerequisite: Proficiency with a martial weapon

Your martial training has helped you develop a particular style of fighting. As a result, you learn one Fighting Style option of your choice from the fighter class. If you already have a style, the one you choose must be different.

Whenever you reach a level that grants the Ability Score Improvement feature, you can replace this feat's fighting style with another one from the fighter class that you don't have.