# You can use which() to find rows with the typo "nnchilled"
which(CO2$Treatment=="nnchilled") # Row number ten
# You can then correct the error using indexing:
CO2$Treatment[10] <- "nonchilled"
# Alternatively, doing it with a single command:
CO2$Treatment[which(CO2$Treatment=="nnchilled")] <- "nonchilled"
# Now doing the same for "chiled":
CO2$Treatment[which(CO2$Treatment=="chiled")] <- "chilled"