Post it in the chess comunity and as a link in my latest chess post, maybe in some other players posts too, do not be afraid, we help you. I will then post a message in the lichess team too. 3 days in advance would be great. Cross post to the gaming comunity, some discord channels and so on. Promoting is part of the game. Look back in time when we started the chess tournaments, we played half a year with a few players only. A good logo picture will help, a fixed day, and so on.