You can reorder the levels of the xaxis factor with the factor() function.
library(ggplot2)
DF <- data.frame(fruit = c("apple", "pear", "cherry"), Value = 1:3)
ggplot(DF, aes(fruit, Value)) + geom_point()

DF$fruit <- factor(DF$fruit, levels = c("apple", "pear", "cherry"))
ggplot(DF, aes(fruit, Value)) + geom_point()

Created on 2019-12-11 by the reprex package (v0.2.1)