How to turn on Instant Replies for your Facebook Page
1. Click Settings at the top of your Page
2. Click Messaging in the left column.
3. Below Response Assistant, click to select Yes next to Send Instant Replies to anyone who messages your Page
4. To change your instant reply message, click Change, update the message and click Save
How to turn off Instant Replies on FB Page
1. Click Settings at the top of your Page
2. Click Messaging in the left column
3. Below Response Assistant, click to select No next to Send Instant Replies to anyone who messages your Page.
Note: Instant Replies aren’t sent when your Page’s messaging status is set to Away and are not included in your Facebook Page’s response rate or response time.
See: How to Delete a Facebook Post on My Timeline