likes messages
Unless the member has also posted a comment you can't 😭 - not directly anyway.😁
You can only go into your own thread and post a Response "Thanks for the 'Like' xxxx", or send 'em a PM (Private Message) if you prefer.
To do that go into [Messages], see boxes at top of the page, select Send New message, type in the User Name of the member and then your response. Cheers, Doug 😎