See How to create numbered headings or outline numbering in Ribbon Versions of Word by Shauna Kelly.
This is what your current list looks like:
00 deleteme 10.png
Only two of your numbering levels are attached to styles and your list is not named.

Your TOC is the following field: { TOC \o "1-3" \h \z \u }

You mean "headings" not "headers." See : What is the difference between headings and headers?



Reference: TOC Tips and Tricks by Suzanne Barnhill, MVP