It's on indesign ME version that support RTL.
It's exactly where the linked help page says it is - if you have the Middle East version of InDesign installed. You probably don't, but you can check by going to Help -> About InDesign. It'll say "Middle Eastern Edition" at the top of the window.
If you are a Creative Cloud member, you can uninstall InDesign, go to the Creative Cloud app, change your language in the preferences to Engish (Arabic), and then download the ME edition with an English interface. (Or with an Arabic interface, of course.)
On ME version of InDesign, Go to Paragraph fly-out menu-> Justification dialog
Now you can set the width of your choice for automatic kashida insertion.