First you must login to your website's ftp so that you can access your files. Once you are in your ftp, look for the .htaccess file. If you do not have one, then simply create one. It MUST be called .htaccess or it will not work properly. Now open the .htaccess file.
Now that you have the .htaccess file open, we need to create our 404 page. In the video below you will see my simple 404.php file that I created for the video. You are welcome to use that example. It was created using Bootstrap. Or if you need a page created please feel free to contact us.
So now that we have our page created, we can get started. Go to your .htaccess page and open it. Copy and paste the following code:
#custom 404 page
ErrorDocument 404 /yourFileLocationHere
Replace /yourFileLocationHere with your own file location. Also make sure the 404 stays there before the link with a space in-between.
Now save your files. And now your website will redirect to this newly created page when there is a 404 error.