In order for you to add a competitor in the Competitors section, they must be a Business Profile! (For more information about why, see here.)
Click on Analytics on your left side menu
- Click on Competitors and then go to the Overview
- Click on the blue '+' at the top of the page
- Enter their exact Instagram username and select them from the dropdown
Please note it takes approximately up to 24 hours to provide the first set of results.