The ending of Fire Force Season 2 in the manga is tied to a crucial event or development. But it's not always a one-to-one match with the anime, as some elements might be reorganized or emphasized differently.
You could start from the chapter where Season 2 of the anime ended. But it's best to check manga forums or dedicated websites for specific recommendations.
I'd suggest looking for manga reading guides related to Fire Force. They often specify precisely where to begin after season 2. You could also ask fellow fans on manga-related social media groups for accurate starting points.
I don't have the exact chapter number off the top of my head. Usually, you can find out by referring to manga discussion groups or official manga release details.