At the risk of stating the obvious:
PM? He may use email notification. Or try to email info@domain.
PM is not possible since the user last active was October 2020 while his last post is on 2019. He doesn’t leave any contact info besides his ANN thread.
His thread receives a lot of pending request like this.
@Yahoo, maybe you can try contacting the registrant info on his domain registration. Here’s his who.is result.
https://who.is/whois/dicesites.com