You don't. The way eBay works is that if an item is not as described, the seller is required to provide a return shipping label or a refund without a return.
You can open an "item not as described" return request, and the seller will have to respond with a label.
As a buyer, eBay expects that you only open a return in good faith. If multiple sellers report that you abuse the return process, you can get removed from eBay's buyer protection. Meaning, you won't be able to make returns in the future.
Most items have a 30 day window from delivery (or 30 days from the expected delivery date if untracked) to make a return. For trading cards, that window is only 3 days. If you cannot open an INAD return, it's possible that the return window has closed.
eBay has two different return policies for each transaction. The sellers own return policy, and the buyer protection policy. A seller telling you that you have to pay for the label isn't relevant to if an item was not as described. That would fall under buyer protection, not the sellers own return policies. This is a common misconception some people have, they think that if a buyer does not offer returns they cannot return an item if there is an issue with it like it is defective or arrives broken.
