Usually, when someone requests a page that doesn't exist, a server will return a 404 (not found) error.
Create them manually in your .htaccess or your NGINX server config
While this is not for the faint of heart, it's often one of the fastest methods available if you have the know-how and the access to do it.


Create them with a redirect plugin
There are several redirect plugins on the market, the most well known one being Redirection. This is a lot easier but has the disadvantage of being a lot slower as to do the redirect, the entire WordPress install has to load first. This usually adds half a second to a second to the load time for that particular redirect.

Some time Google discovers pages in weird ways. Though 404 in webmaster is not an issue at all. But still you can use plug in or place redirect in .htaccess file helps to reduce 404 in webmaster. Though I want to reiterate, you don't need to worry at all even if you don't do anything and keep as it is. Increase in 404 don't impact your ranking anyways.

If the 404 pages link are not present in your web page's html, you need not to worry about. It seems annoying in your webmaster account but will be harmless (if not originating from your website).

An interesting read on the topic,
https://www.seroundtable.com/google-...ult-23226.html