...
This should only need to be done once.
Additional steps/notes:
If holding CTRL on your keyboard does not load the "Choose R Installation" Please search for the On-Screen Keyboard within Windows start menu, and use this. Pressing the Windows Key on your keyboard, or clicking the menu on the Desktop, type "On-Screen Keyboard"
If changing the version of R and Rendering Engine still does not work, it has been reported that changing to an older version of R and back to the latest launches RStudio again.