You are likely thinking of the original PC game, or the movie tie-in game The Last Airbender (2010) . Fans also frequently confuse the franchise with James Cameron's sci-fi film Avatar , which had a major game release around that era.
The game features the original voice actors from the animated series, which goes a long way in making it feel like a lost episode. Download avatar: The Last Airbender PC Game 2011
🕹️ Avatar: The Last Airbender (PC, 2006) - Detailed Review You are likely thinking of the original PC
You can swap between 4 characters. Aang uses mobility and airbending, Katara acts as a healer, Sokka handles ranged boomerang attacks, and Haru provides heavy Earthbending combat. Katara acts as a healer