cancel buy it now purchase

[kswteach]

I was watching two similar items. I chose the wrong one and hit the buy it now button. I realized it and then purchased the other similar item. I no longer need the first one. I just realized that the seller opened a case for the unpaid item. I have contacted the seller and they agree to cancel the sale since I don't need the item. However, they are asking me to contact Ebay to get that done. They don't know how to cancel it. I am not sure what to do.