Change limits of legend bar using factoextra ggplot2

I'm performing a PCA using R. I'm drawing a biplot of the PC1 and the PC2 using factoextra as in this example.

library(factoextra)

# Load decaathlon2 data
data(decathlon2)
decathlon2.active <- decathlon2[1:23, 1:10]

# PCA
res.pca <- prcomp(decathlon2.active, scale = TRUE)

# Plot
fviz_pca_var(res.pca,
             col.var = "contrib",
             gradient.cols = c("#00AFBB", "#E7B800", "#FC4E07"),
             repel = TRUE)

How can I change the limits of the legend bar? I would like to define the limits between 5 and 10, instead of the current [8.8, 9.4].

The example you gave does not have the stated range of [8.8, 9.4] - presumably you are referring to a different plot created from your actual data. Setting the color range to [5, 10] in the given example would leave some of the arrows uncolored (since some of the contributions are greater than 10), so let us demonstrate by increasing the scale of the color bar in the example image from [6, 12] to [0, 15].

To do this, you can add a scale_color_gradientn to the plot, specifying your own limits. Use the same colors you passed to gradient.cols:

fviz_pca_var(res.pca, col.var = "contrib", repel = TRUE) +
  scale_color_gradientn(name = "contrib", limits = c(0, 15),
                        colours = c("#00AFBB", "#E7B800", "#FC4E07"))