All theres guys are wrong. Here's what you do.
Sorry there was no edit button.
This is how I do it on Mac.
/Applications/BlocklandLauncher.app/Contents/MacOS/BlocklandLauncher -dedicated -map skylands
In terminal
Do not change any of that. Just put it straight in terminal. Once it's done you can join the server and change the map ad other stuff.
Hope this helps.
PM me for any other questions! My in game name is Pinkie Pie!
-Stunty