@swifto look at Add "Site search" in "Search engine" option. no examples no idea how to setup - #2 by Saoiray
Then kind of How do I use a custom search engine? - #8 by Saoiray
It’s instructing clearly. Go to the website you want to add and do a search. So when I did a search for Swifto, the URL changed to https://yandex.com/search/?text=swifto&lr=113211&search_source=yacom_desktop_common
The instructions are to replace your search term and everything after with %s
So https://yandex.com/search/?text=swifto&lr=113211&search_source=yacom_desktop_common would become https://yandex.com/search/?text=%s
So on the third part, you put https://yandex.com/search/?text=%s