In order to create custom error pages in cPanel:
1. You need to go to the Error Pages icon and click on it.
2. Soon the page will appear where you can generate custom error pages and you can also add one or more tags in order to customize these pages further.
3. Enter some texts if you want and then click on the save button.
4. With this much of task, you will be able to generate custom 404 error pages.
5. You can even customize some other error pages as well. All the other accounts come with the preset error pages.