IMPORTANT: Before starting out, please make sure you do have the ability to install plugins, or FTP access, if you don’t, you will need to contact your host either way, so you’re best off requesting them to update the 404 page, they should be able to help you out.
Step 1: Getting code
Start off by going to the website: notfound.org
Next up is choosing your local country. If you blog using the English language, you’re best off using the “other countries” as choice, even when located at the United Kingdom.
This should lead up to a new page, simply press the “Yes, I’ll make better use of my 404-page” which should make the register website option appear.
Register your domain or subdomain, this is the top-URL of your blog, like in my example would be “snowcalmth.com”, but could also be “blog.snowcalmth.com”, however, do not add the backslash “/” or anything that is after the backslash.
After pressing next, you should see two possibilities, for this usage you will need to copy the code, you won’t have to download the page itself.
Step 2: Creating page
Next up is going to your blog.
Start by creating a new page, not blog post, set the editor to text instead of visual, if needed, and copy the previously copied code to the editor.
If needed you could add more text to it, but do not edit the code you pasted a moment ago, this could cause problems.
Add a subject, make certain your permalink is correct, setting it to “404” is the most common practice.
Press the publish button and go to the page you just published to check if it works.
Step 3: Installing plugin and setting it up
Next up is adding a new plugin, this should at most hosts be available without FTP access, however, at some hosts this may be different.
To learn how you can add plugins, check WordPress’ official tutorial at: https://codex.wordpress.org/Managing_Plugins
The plugin that I use, and tends to be the most user-friendly, is the “Custom 404 Pro” plugin by “Kunal Nagar”
After installing this plugin, just hover the button it creates at the sidebar of your admin area and click settings.
Set the mode to “wordpress page” and select the page you created before.
Press save, and…
NOTE: The page creation could be ignored, and instead you could upload the page through FTP and set the URL of it through the plugin I said before, this however will make the 404 page to be independently shown of your website or blog, causing annoyances to the visitors of your website or blog.
Now you’re able to enjoy using your blog or website with the knowledge you are helping out missing children.