How do I give back the money I received after a conflict was resolved?

[lier1]

Back in November I ordered a shirt that never came, so in February I opened a conflict to get my money back. Which I did, money is here, conflict is resolved. But yesterday (April) the shirt actually arrived! 

Now what do I do?

Do I just keep the money or is there a way to reverse the conflict? I would like to give the money back to the seller, since they did deliver (better late than never).

[sharpiemarker]

@lier1 

Contact seller through the transaction details by email or messaging asking to confirm their PayPal email address so you can resend payment to them.