Sorry, but this is beyond my ability to help with here and all I can do is tell you what needs to be done.
In the walker, when the menu item is shown you need to get the current logged in user id and check the field and show or now show the menu item. This will likely require added these checks to both the start_el() and end_el() functions of your custom walker.
Welcome to the Advanced Custom Fields community forum.
Browse through ideas, snippets of code, questions and answers between fellow ACF users