Then insert a blank paragraph styled as Heading 3 after each Heading 2 paragraph. Modify the Heading 3 style's font format to be hidden. While there, have Heading 3 restart after Heading 1 instead of Heading 2. Assuming that Heading 1 is for the chapter, Heading 2 is for the section, and Heading 3 is unused, modify your multilevel list so that Heading 3 has the same number formatting as Heading 2. For this to work, use chapter numbering with page numbering. Note that you need to press Ctrl+F9 to get the braces. In this case you would want to enter the field manually, like so: However, if Chapter 1 starts on (for example) section 2 of the document, you will need to nest the Section field into a formula.
right-click on the style you want to delete, then select Delete