The Covers and Highlight Names are extremely important to your account as they are the first things a new visitor sees on your Instagram profile.
Here's how to add a Cover to your Instagram Highlight:
1| Add the images you wish to see as a Cover to your phone's camera roll
2| Tap and hold the Highlight to you want to edit
3| Click "Edit Highlight"
4| Click "Edit Cover"
5| Select a picture from your camera roll
6| Click "Done"