I assume that the problem is the doubled number on the first entry.
Try attaching a document with the problem, perhaps one where you strip out all but the heading.
How to attach a screenshot or file in this forum.

Resources:

• Generating a Table of Contents - Complex Documents
• How to create a table of contents in Microsoft Word by Shauna Kelly
• TOC Switches by Suzanne Barnhill
• How to create numbered headings or outline numbering in Ribbon Versions of Word by Shauna Kelly