How to use OnKey in your messaging apps
OnKey is a keyboard, so it works in any messaging app that has a text field. You do not leave the conversation.
Steps
Open the conversation and tap the message box. Write your message the way you normally would.
Hold the globe key and pick OnKey. The OnKey strip appears with Fix, Tone, Reply, Translate and Summarize.
Tap an action. To reply to a message you received, select or copy it first, then tap Reply.
Insert the result. Read it, then tap Insert, or Undo to keep your original. Then send as usual.
Questions
Does it send my messages?
No. OnKey never sends your message. You send it yourself.
Does it work in every app?
It works wherever iOS allows a custom keyboard. iOS uses its own keyboard in password fields.