Send the buyer a message apologising for the delay but you are pleased to see that your tracking for the item has shown delivery and can they now kindly repay you.
The repayment cannot be done through eBay, so you and the buyer have to agree whih suits you best, be it by cheque, bank transfer, or a PayPal Friends and Family payment. Or you can send them a PayPal invoice to pay you.
There's nothing to enforce this payment, but most people are honest and wouldn't want an item for nothing.
If PayPal is used, email addresses need to be exchanged, this can sometimes be found with the order details >> Show Contact Info. If not and you need to ask the seller for this, make it very, very clear in your eBay messages, as eBay do read these, the reason for these exchanges. Make it clear it's not to be used for an off eBay sale.
@emmakibble12