Carl was accidentally bitten by a walker when he picked up Siddique in the Woods. Carl pulled out his pistol with all his last strength, and ended his life before he changed.

Detailed process:

In "The Walking Dead Season 8", Carl played by chandler riggs is one of the core members of Rick's team, Rick's son. Carl is a curious, clever and naive boy. After many hardships, I gradually grew from a child to an independent big boy. In the ninth episode, Carl was accidentally bitten by a walker when he picked up Siddique in the Woods.

But Carl didn't tell his father, but chose to spend the rest of his time saying goodbye, such as completing the task of protecting the community that his father told him before he left and writing a farewell letter to everyone who loved him. Rick wants to treat Carl, but Carl is getting weaker and weaker. Rick had to give up and chose to take Carl to the dilapidated church. Carl pulled out his pistol with all his last strength, and ended his life before he changed.