The Author settings under the source’s Advanced tab allow you to manage how authorship is credited for all the imported content from that source.

Credit the Original Author
This setting determines how the author of the imported content is credited.
- Credit the original author: This option credits the original author of the content, based on what is provided in the source’s RSS feed, as the author of the content on your site.
- Credit a user on this site: This option allows you to credit a specific user on your own WordPress site as the author of the imported content.
The latter option is not used often since you would be taking ownership of content that may not be your own original work. That being said, it could be applicable when you also own the original content you’re importing.
Credit Method
If the source feed author isn’t an existing user on this site, Aggregator will assign imported items to a new “Source Author” user – the default method. This user will appear as the original author’s name on your site.
Alternatively, you can create a new user for each source author or use a single fallback user for all imported items.
Fallback User
This setting specifies who should be credited if the imported item has no author or if the author does not have a WordPress user account on your site. You can select any user from your WordPress site to be credited as a fallback, including yourself.