The package `stdmod` can be installed directly in R:
https://cran.r-project.org/package=stdmod
More on the issue:
Cheung, S. F., Cheung, S.-H., Lau, E. Y. Y., Hui, C. H., & Vong, W. N. (2022). Improving an old way to measure moderation effect in standardized units. *Health Psychology, 41*(7), 502–505. https://doi.org/10.1037/hea0001188
A quick start guide can be found here:
https://sfcheung.github.io/stdmod/articles/stdmod.html