When you set a conversation in your Engage Inbox to ‘close’, you can always go back and set the status to ‘Open’ again to come back to it at a later time.
To do so, set your filter to the ‘close’ status. You’ll now see all the conversations that have been set to ‘close’.
Here, click on the conversation you want to set to ‘ pen’ and simply click on the 'box with an upward arrow’ icon from the top right corner of your message window.
That will set the status of the conversation to ‘Open'
You can also use the Keyboard Shortcuts in Engage Inbox to close the conversation.
The shortcut to ‘open’ a conversation is ‘o'.