How do I move items from Sold to For Sale?

Disco Stu

I was selling an interior and somebody showed an interest and said they were going to have it. I marked it as sold and it got moved to the 'Sold' noticeboard. They have now informed me that they no longer would like the interior, so I wanted to mark as 'un-sold' but I can't. Is there anyway of moving it or do I have to create a new message?

Many thanks in advance