Hi Lynnette. Beware spending money on vinyl repair kits. They might cost more than a new seat would cost.
Lynnette, this is one time I suggest you just throw the old one out and buy a new one. For two reasons---- first, the tear (and repair) could cut someone or seriously scratch whoever sits on it and second, what you use to repair it could also irritate or cause an allergic reaction to someone sitting on it. It's not worth it----I would just replace it.
Naomie gave you a good set of instructions on the "how to's" of vinyl repair.
I would question why go that way because if your toilet sear has ripped in 1 spot from general usage in a concentrated weight bearing area, it is most likely weakened and/or brittle, making me wonder it the vinyl repair would be effective. The quality of the vinyl may not be a good candidate for repair at this point.
You can get a new one for $7 or $8 dollars