The author of a blog post will be automatically assigned to the users that has created that blog post. If you want to change this, go to “Blog” on the left-hand side menu below “My Site”.
Select the blog post you would like to change the author of by using the underlined text.
Once in the blog editing area, go to the “Meta and Social” button at the top.
Now in here, scroll to the “Author” dropdown.
Select the name of the person you would like to set as author and ensure you press “Save”.