Go to Send messages app via the menu in the top left corner
Type your message text On entering text for the new message, other message options are shown. One of those options is Enable replies.
Enable replies by changing the slider
From No to Yes
Choose a sender
Using replies requires a specific sender name. Therefore, sender names are limited when switching on replies. Choose a sender name by selecting a Sender.
Complete your message
Add recipients and click the Send button at the bottom to send your message.
Go to Received messages via the menu in the left top corner
With replies enabled, recipients will be able to reply to your message up to 72 hours (3 days) after sending. Replies to messages will be shown in your Inbox which you can visit via the menu.