Install the package from CRAN:
install.packages("regress")
Alternatively, install it from R universe:
install.packages("regress", repos=c("https://kbroman.r-universe.dev",
"https://cloud.r-project.org"))
Or use remotes to install it from its GitHub source:
install.packages("remotes")
remotes::install_github("kbroman/regress")
Clifford, D., & McCullagh, P. (2005). The regress function. The Newsletter of the R Project Volume 6/2, May 2006, 6. (link)
Forked from David Clifford, but now maintained by Karl Broman.