The buyer (not you) needs to open a return case through Ebay.  They should choose the reason 'arrived damaged'.

Then, if you used your own postage, you will have to refund the buyer and claim from the carrier.

If you sent using Ebay Simple Delivery, Ebay will deal with the claim.  They will refund the buyer without needing them to return the item and you will keep the buyer's payment.

Either way, it needs to start with the buyer opening a return case.

Edit

As you are a business seller, you will have to refund the buyer and claim against the courier - check their Ts and Cs to make sure glass items are covered.

Just to add, if you used Yodel, they don't seem to cover glass and glassware.  This is between you and the carrier; you won't get any help or compensation from Ebay.  Check which services do cover glass if you are selling a lot of glass items.

Buyer needs to open a claim and  report item arrived damaged, you can then  issue a return label or just refund via the case and claim from your carrier if they cover glass items.