Changing default search engine on Safari

Hello, I want to change in my Safari (on mac and iphone) default search engine. But I do not have option to use my preferred search engine, which is seznam.cz. Can anybody tell me, what to do, how to contact apple's developers to add this search engine into Safari? I know there is an option to use different browser, but I would like to use Safari still, because I like the interface of it.

Thanks!