When you get it back cancel/refund the transaction via the dropdown menu arrow for the item on your orders list.
If you want to continue with the buyer they should update their address on ebay. Then you can relist the item for them to buy again.
If you prefer not to sell to them put their ID on your blocked bidder list:
https://www.ebay.co.uk/bmgt/BuyerBlock
and leave it at that.
@neho-89