How posts move to each sub-directories after migrate to multisite?

Hello,

My current blog is running by a few authors. The posts are mixed together.

I am planning to “migrate” the current blog into a sub-directories multi-site. This way each author has his/her own sub-directory blog. However I have a question before doing that.

How can the posts move to the sub-directories that belong to each author?

Thanks and best regards