how to tell google that it is not an error page - wordpress seo 404 page

how to tell google that it is not an error page - wordpress seo 404 page

hello seo / wordpress experts, I greatly appreciate your help in advance.
I did a little modification to the 404 page in wordpress in order to
create a customized url.
for example, i modified the 404 page so that instead of showing "page not
found" it actually delivers useful information to the users (i did a parse
in the url to show useful information)
but when I submitted some url to the google index, i think the crawler
sees it as 404 error.
i definitely want to keep it as it is otherwise i would be creating too
many pages.
any comments or suggestions are appreciated. basically my goal is to tell
google that it is not an error page but it is good page.
thank you