install.packages("asreml", repos = "https://products.vsni.co.uk/asreml/r-package")
This points R at a real CRAN-shaped repository (src/contrib/PACKAGES under the hood) — install.packages() resolves the right build for your R version and OS the same way it would for any CRAN package.
See also: R version compatibility.
library(asreml)
asreml.license.status()