Order graph x axis barplot

General
,
2

Setting the factor levels should work. Try the following example.

library(ggplot2)
library(dplyr)
FC <- data.frame(Probiotics = c("Control", "YUN_S1.0", "AMB_F471",
                                "AMB_V001", "AMB_V038", "HAN016", 
                                "HNP007", "CON21"), 
                  Concentration =  c(2, 2.4, 3, 2.6, 2.4, 3.2, 2.2, 3))
ggplot(FC, aes(x = Probiotics, y = Concentration)) + geom_col()


FC <- FC %>% mutate(Probiotics=factor(Probiotics, 
                                      levels=c("Control", "YUN_S1.0", "AMB_F471",
                                               "AMB_V001", "AMB_V038", "HAN016", 
                                               "HNP007", "CON21"), ordered=TRUE))
ggplot(FC, aes(x = Probiotics, y = Concentration)) + geom_col()

Created on 2020-04-11 by the reprex package (v0.3.0)