Change Author of a Post?

Hi all,

I’ve making a new website where the normal users (not authors) send post with a specific form and i receive the post in the panel, for now is OK!

My problem is because i want to use a Custom Field to define the author of the post (the user who send the entry) because if the user is registered they have a own profile page that show all the posts with the information

I can change the author with a dropdown menu, but only with admin/author/co-author users and i don’t wanna to give more user level because the site will get too many users (thousand for example)

There is any way to do this? using Custom Fields to assing one post to a user? or any plugin?

Thanks!
Greetings!