Stable download URL for the latest version of Rtools42: https://github.com/r-hub/rtools42/releases/download/latest/rtools42.exe
The latest development version: https://github.com/r-hub/rtools42/releases/download/devel/rtools42.exe
For all versions see the releases: https://github.com/r-hub/rtools42/releases
See https://cran.r-project.org/bin/windows/Rtools/ for the official web site to download Rtools42.