Returning an item - how do i change carriers AFTER clicking "print shiping label"?

[karengarys]

I am returning an item.  I clicked "print return label", and got the USPS label.

I later learned the seller wanted me to use UPS instead.

I took it to UPS and shipped it.

How do I connect the UPS shipment to the return?  There seems to be no way to un-do the shipping label on the return-in-progress.