Hello Pratik,
Thanks for writing to us. Are you using the latest version of plugin (v1.1.1) as in this version fix was given to menu scroll issue on iOS devices. In the latest version of plugin, if left menu is bigger then a scroll bar is added to the menu so that when user scroll down to the content then they should be able to access the fixed menu at left/right side by separately scrolling the menu.
Menu scroll is not by default visible, when you will hover on menu or try to swipe it, it will start appearing. If still the menu scroll does not appear then please send us the link where you have added the documentation, I will look into the issue.
Waiting for your response,
Thanks for all your patience.
Best Regards,
Sampada,
Documentor Support Team.