Search results – 404 error after hitting enter

So I am using a theme from envato and there’s extremely poor response from the support team and I hate not trying things on my own.

On the website I am working on right now there’s a problem with search page and search results.

When going into search and typing, you can clearly see that there are some matches (let’s say “sport”) but when hitting an enter/search button the page goes straight into 404 error.

I when you perform search on the 404 page, the search is available but the result page goes bollocks!

Any advice on how to work on it without access to search.php (blocked by the owner of the theme)

page address: https://youthtalkedinburgh.co.uk/
theme used: Kleo