Add redirect though functions.php?

Hello.
We have a system that imports about 120 posts per day with WP All Import.
Sometimes posts are duplicated and we are checking them with a custom ID inserted as a custom field in the post.

The problem is that we need to delete the older post and put a redirect to the new one, this during import.
We can write our custom php functions in WP All Import, so we asking here how can we add a new redirect by editing our functions.php?

Thank you in advance.