He needs to go https://delete.nostr.com and paste in the event id which is 8ec2959fc5e2b1156f9371de67b7c645fb19baa5b39bdd56cc519039cb2c6c57
I got this from my phone by taking the naddr and pasting it into a njump.me URL and it lists the I'd.
Using that rather than the naddr will mean he could issue an annoucement with that identifier later.