How to replace Apple Pencil Gen 2 from Amazon

You will need to seek assistance from the retailer from whom you purchased the incorrect Pencil - in this case, Amazon.

Unless you are making a claim under Apple’s limited one-year product warranty, Apple will not “exchange” products purchased in-error through third-party retailers.

iPad5 does not support Apple Pencil. For future reference, here is link to the full compatibility list for Apple Pencil and iPad:

Apple Pencil compatibility - Apple Support

Have you checked to see if you can return it for an exchange or refund?

Often there’s a date before which an item can be returned even from third party sellers.