In Core Keeper, the first player who joins the server, which is usually the server owner, will be granted admin permissions by default. If you want to grant more players admin permissions, it's easy to do so in game.
1. Join your server as the character you first ever connected with. This account will have admin permissions by default.
2. Press ESC
on your keyboard to open the game menu.
3. Under Connected Players on the right, you can toggle this star to enable or disable admin permissions.
4. You can now choose who you would like to be an admin.