Have Advanced Custom Fields data populate redirect database

I’m running the Advanced Custom Fields plugin. While someone’s posting a new post, I’d like them to be able to have them choose a user from a dropdown (I have that working already) and when the post is submitted, the selected user is assigned the post URL as their redirect. Advanced Custom Fields returns a variable for the user selected, so I just need to know what to do with this variable to assign it the current post URL as their login redirect.

http://wordpress.org/plugins/peters-login-redirect/