When you say "the previous thread" it would help if you gave us a link to that thread. If my response does not give you the help you need please either post a response with a link to that thread or edit your previous post to show it.
In inserting the Caption, you need to click on the Numbering button and then check the box to include chapter number. You need to associate this with a particular numbered style. You would want to use the full stop (period) as a separator.
How to create numbered headings or outline numbering in Ribbon Versions of Word by Shauna Kelly
Insert a Caption - Complex Documents in Microsoft Word