Charlie Francis body was found in series 2 which the group found. All at a suden ins s2ep11 he's walking around the office, have I missed something?

The episode in which you saw Charlie alive is actually an episode from season 1. Fox never aired it during the first season, and, for some reason, decided to air it in the middle of the second season.

I remember when Olivia shot him in the alley and he died, then all of a sudden he appeared at the office as if nothing had happened. I don't think I've missed anything, but I don't know what happened.
Can someone help us, please? :/