Use the For Each action with the Substrings In collection. The example on the wiki page for the collection shows how to loop through each number in your text. Whether it is return or space separated wont matter.
The for each number, use the Insert Text by Pasting action to paste in the text, and the Type a Keystroke action to type the Enter key. I would suspect you probably want to add a Pause action to ensure you don’t enter the numbers too quickly, but it depends on the target application.