If you only edit some text simply, please install the Loco translate plugin to replace the text.
You could edit the 404.php(Appearance>Theme Editor) directly if you want to edit more things. (Please install the child theme, put the changed 404.php into the child theme folder. Or it will be covered when theme update.)
Basically I want to change the message from this page (404 error)
I have installed child theme I go to theme editor and it shows me this this has a problem the prototype is missing.
and.
I downloaded loco translate where exactly I can replace the text?
If you use the child theme, please please log in FTP to upload the 404.php to child theme folder(please login host cPanel to find FTP). You could edit the 404.php in the child theme.
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