In this day and age if you want to advertise and bring in new players there a ton of ways to do so.
Bottom line is you can advertise with Youtube make an appealing trailer for the game use it on youtube ads
Contact MMORPG streamers on both twitch and youtube platforms
reward systems
But we have to be very realistic the game is Donkeys old and there are just new titles coming out.
but there are still players that will want to play this title