I created a league and it’s a private league, then I accidentally resigned from my club!
Who would be the new creator to send the request to, or how can I manage my team again?
OSM will be the new league moderator and since it's a private league no one would be able to join the league again because OSM does not send invitation to join leagues and neither does OSM accept request or Grant permission to join leagues, only human managers can send invitations, accept request and Grant permissions.
Also, it is not possible to rejoin a league which you previously resigned from. Sorry, but you have to join a new league now.