There are some existing posts about using R in databricks:
https://docs.gcp.databricks.com/en/sparkr/index.html

https://docs.databricks.com/en/dev-tools/databricks-connect/cluster-config.html

Once you have the correct cluster started (this post is about an error I encountered, you must make a personal compute: https://community.databricks.com/t5/data-governance/recommended-access-mode-for-multiple-users-with-...), using R is easy. You can just start a notebook with R syntax and it should automatically recognize that you're coding in R.

But hopefully you've already figured it out by now..