You would have to
- Query All Posts and loop over them
- Get the value of the text field for each post
- See if there is a term that matches the text field
- If there is no term then add the term
- add the term to the post
You would need to create an “init” action that does the above and then once completed remove the action.
If you have a lot of posts this could time out. In this case you would delete ACF field after performing the update and in your query you would only get posts where the meta key exists. Then you reload the page until it does not timeout and this will mean that all posts have been migrated and you can delete the action.
