How do I restore the return key on my iPhone keyboard?

When using some apps (ei. messages, instagram, cai, email, etc) I am unable to find or use the Return Button, as it's completely replaced with a send button. I need the return button for captioning, but am unable to find or use it in any sort of way. I don't want to constantl have to switch apps just to write something out, what can I do to constantly have the Return Button on my keyboard?

[Re-Titled by Moderator]