Install native ARM R: https://cloud.r-project.org/
Install RStudio (probably preview) which is not native as of today: https://www.rstudio.com/products/rstudio/download/preview/
This blog post is helpful for getting Tensorflow working, but it is older, before the ARM version of R and the RStudio version that supports it was available.
This other blog post has specific steps outlined, but some of it has also been superseded.