In WordPress, you can assign/switch posts from one user to another.
For instance, this post is authored by Ediko, i can assign this post to any other user of this site. you can move or assign as much as twenty posts to another user per time.
I will assign 2 posts from Ediko to Techs Jardin at the same time.
From your WordPress dashboard, Click on Posts and All Posts, you can also assign posts by category.
Check the posts you wish to move to a user and under Bulk actions drop down, Click on Edit and click Apply.
From the options that pops up, under Author, select the author you wish to assign the posts to, you can also change the categories of the posts in bulk and click on update.