Just to add to what MozBoz has already said, you can also set the author from the post / page in WP directly. You can usually do this from the editor itself, but there are a lot of page builders available, so I’d suggest going to WP Admin and to your All Posts, hover over the post you want to set the author of and select Quick Edit. This will pull down a tray of options, one of which will be an author dropdown where you can select the posts author from all of the users on your site.
