itch.io

The dev commented how to do it simply hehe "Go to System Preferences -> Secutiry & Privacy  -> "Open Anway"  -> (Type  in password)" (Nacho Sama) 

Just incase if you haven't found out yet, but you need to try and open the app. 

Open the app again, then when the warning pops up - press cancel. 

Go into your System Preferences, click onto Security & Privacy. 

Then go onto general, it should have some message something similar to you can't open "That's not my neighbor" due to having a non-verified developer. 

You can press on open anyway and see if it lets you open it. If it doesn't then -

You need to click on your lock on the bottom and input your computer password. 

Then press open anyway, and then the app should work. (Don't forget to put the lock back on after your done). 

Then you should be good. Hopefully this helps and sorry for it being too long.