how?

Scratch's coding language is not based on text syntax. That being said, one couldn't prompt a new line. All you have to do is stack code in the form of blocks like a jigsaw puzzle.

It is possible. Here are the steps on how to do it:

• Create a new project.
  
• Create a new variable. It will contain the new line character, so name it something that represents that, like newline.
  
• Put this block in your project, but don't run it:
  

  set [newline v] to [SOMETHING_RECOGNIZABLE]

• Save the project to your computer.
  
• Rename the file from xyz.sb3 to xyz.zip.
  
• Drag out the project.json file onto your desktop.
  
• Right click > Edit that file.
  
• Search for SOMETHING_RECOGNIZABLE and replace it with:
  

  \n

• Save the file.
  
• Drag the edited file back into your xyz.zip.
  
• Rename xyz.zip back into xyz.sb3.
  
• Open that project.
  
• Click the block to run it.
  
• Now the newline variable should contain a new line - try it out using the following:
  

  say (join [Hello] (join(newline) [world]))