[Theme Horse Support Team]

Hi liljeroos,
First of all you need to unhook the functions in child theme functions.php Then only you can change the code.

Here is the link which may help for you. Yes exactly don’t copy all the functions just copy only the functions which you want to change.
For more information.
https://www.themehorse.com/support-forum/topic/change-404-text/

If you are still unable to unhook and change the code then you may hire a developer to fix the issue.

Thank you!