While you are editing or creating a new post, you can add an existing author or create a new one while editing your post.
Existing Guest Author
Scroll down to the ‘Select a Guest Author’ metabox. To select an existing author, choose ‘Existing Author’ and select a guest author from the dropdown list.
New Guest Author
Select the new author option box. The fields for the guest author will be displayed.
Enter the author name, details/bio. Click on the upload image button and choose an image from the media library or add a new image. You may also fill out the alternative details. See Adding and Editing Guest Authors for more details.
Once the post has been updated, the guest author will now be the selected ‘existing’ guest author in your post and the new guest author can be found in the Guest Authors list.