Use scale_y_reverse()
, take a look at this example:
library(ggplot2)
sample_df <- data.frame(
x = 1:10,
y = 1:10
)
ggplot(sample_df, aes(x = x, y = y)) +
geom_point() +
scale_y_reverse()
Created on 2022-01-22 by the reprex package (v2.0.1)
If you need more specific help, please provide a proper REPRoducible EXample (reprex) illustrating your issue.