Hello,
Since Parallel was built as a one-page theme it is not possible with it’s current configuration.
However, it can be done.
You will need to create a separate page template and insert a sidebar into it.
This will require customizing the theme files and a basic knowledge of WordPress core and PHP code.
Here are a few links which may help you,
https://www.ostraining.com/blog/wordpress/custom-sidebar/
http://www.wpbeginner.com/wp-themes/how-to-add-dynamic-widget-ready-sidebars-in-wordpress/