And my powers of ESP are not sufficient to guess at your data. If the help page at ?forcats::fct_relevel, doesn't help perhaps consider posting a reproducible example (instructions).
If I had such a reprex, I would probably have caught the typo, and did you read the help page at ?forcats::fct_relevel? If so maybe you could catch the typo? Not being facetious - I know that when you are learning R the help files are very difficult to get to grips with, but it is well worth learning to read them as early as you can.
The problem might be that the column was missing from fct_relevel. Try this instead,
mutate(disprt, group = forcats::fct_relevel(group, "Control", "Coccidia", "S. Typhimurium"))
You could also try the base equivalent which will look something like this (again, I'm guessing because I don't have an example of your data)
disprt$group <- factor(disprt$group, levels(disprt$group)[c(3,1,4,2)])
Posting a reprex is a pain (I know) but you will get the correct help much quicker if you provide one for future queries (or if this still doesn't work).