Sorry, I took out the level editor because it wasn't up to the standards of the rest of the game. I was really excited about including it but it would have taken so much work to add all of the missing features, to add controller support, to get rid of the big JSON window, and to make your levels playable and shareable in a practical way.
I'm really sorry if this ruins your enjoyment of the game! If you really want to access the level editor, it is still in the source code. You can install Godot 3.x, download the TurboFat source code and run the LevelEditor.tscn scene. I can give you more detailed instructions if you're interested in pursuing this. I'm sorry again!