I will assume that the seller sent you the incorrect size of wheels, not that you ordered the wrong size yourelf.
In this case, unless eBy acknowleges their mistake (unlikely) and makes an exception for you, there is nothing you can do to return them through eBay.
If you paid by PayPal, you may still ne able to file a dispute under their buyer protection policy. Or if you paid by credit or debit card you can ask your card ussuer for help.
If this was a UK business seller and you paid by credit card this provides additional protection for purchases over £100 which might even cover the cost of returning the wheels. Otherwise you will probably have to pay the cost of return, which eBay would have required the seller to meet.