Tablet Covers can be expensive and get a lot of abuse protecting your tablet. A little maintenance can extend the life of your tablet cover. Buy a can of "Liquid Electrical Tape" from your favorite hardware store and apply sparingly to the damages edges using the brush attached to the inside of the lid; following the instructions and cautions on the can.
Once dry, apply a second coat to complete the job.
Of course this best on a black cover but there are equivalent products in a few other colours.
First coat applied to the edge.
Corner with second coat applied to the right edge. More coats can be applied if there are gaps but don't over do it or it may be more like a tape than a repair that blends in to the cover.
Let it dry well before putting your tablet back in the cover. Wouldn't want any black stuff on your glass!