Hi @alli23880
That is a crack in the screen. It will have to be replaced.
There's no warranty cover for that.
The relevant part of the manufacturer's warranty states in part: "The Limited Warranty described herein does not cover: (a) damage or malfunctions caused by accident, misuse, neglect, abuse, acts of God or other external causes; .....".
You can check what the warranty for the tablet shows for your location as not all warranties are the same.
Here's the ifixit Kobo Libra Colour Screen Replacement guide that may help
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