Question: how to install rgtk2 package?
Answer: Install R. Download and run the self installing executable to install R (verison 3.5. ... 
Install RGtk2. If you wish to utilise the rattle graphical user interface then you will need to have RGtk2 package and the GTK+ operating system libraries installed. ... 
Install Rattle. ... 
Optional Configuration and Installations.