Unable to downgrade Rstudio to Rv3.6

I downloaded RV3.6.3 from R for macOS , after which I dowloaded Rstudio (RStudio-1.3.1093.dmg) , however the default of 4.1 is getting dowloaded .
I have also tried using rswitch to launch the current version 3.6 but its still defaulting to 4.1

ln -s /Library/Frameworks/R.framework/Versions/3.6

is also not resolving issue

Kindly help !