I removed the link to your site because in this case it won’t help to solve your issue.
Search boxes use backend code to work and we do not access to that code. There’s little chance that we can help you with this little information and a link with a code we can’t see.
Did you post in the correct category? This is the HTML/CSS category, and your search function is likely what’s broken. What’s the language it’s written in? PHP? Might want this thread moved to a more appropriate category.