Making relevanssi work with theme search

Possibly yes, possibly no, hard to tell anything more exact without knowing anything about the search bar.

Is it perhaps an ajax search? Those often assume WP search and interface directly with the search. They can sometimes be fixed to use Relevanssi by invoking the Relevanssi search engine directly.

But, like I said, without any further information, this is the best I can do.

Here is the website, keep in mind that it has adult content: https://escortelegant.com
It does seem to be an ajax search from what I can tell

Also for, https://www.relevanssi.com/user-manual/installing-relevanssi-and-adjusting-the-settings/

where do I add this code?

There’s no code on that page, so I’m not really sure what you’re referring to.

Anyway, I took a look at the site. It has such a complicated search that helping you make it work with Relevanssi is a lot more work than I’m able to do here for you. You either need to be a skilled WordPress developer or hire one to set it up for you. Even then, it’s a type of search that is somewhat poor match to what Relevanssi does.