I was trying to figure it out myself, hence how I landed here.

If you type out your headings in separate lines:

Heading 2
Heading 2
Heading 2

Then go to your Table of Contents to refresh it so that they are all on it, you want them to be on the same page, and the page they will actually land on. I suggest doing this when you're done adding content or close to.

Go back to your headings, pick the line you want them on, hit tab then highlight and drag the next one up to that main line, hit tab, do the same with the next etc.:

Heading 2 (your needed tab space) Heading 2 (your needed tab space) Heading 2

If you need to refresh you table of contents, select numbers only. Which is why suggest you already have most of your work/ all your headings in place before doing so.

I realize I'm late to the discussion but I hope this makes sense and is helpful!