You can find Respond Later feature from the message right-click menu.
Tag Respond Later to the received messages.
You will see a dotted red-colored circle tagged to the message.
To reply to the tagged Respond Later messages, you can scroll up/down on the chat window, or filter the tagged Respond Later messages by clicking on the Respond Later filter icon from the Advanced Filter Group.
Once after you replied that tagged Respond Later Messages, the red-colored circle which was tagged to the message gets auto-cleared.
Or, you can manually clear the Respond Later tag from the message right-click menu when you no longer feel the necessity of Replying to the tagged Respond Later message.