While there isn't an NVDA command for this, it is possible in Word:

1) Press CONTROL+H (This is the replace command, but it ensures the dialog opens, rather than the task pane)

2) Press ALT+M to activate the "More" button to show more options (if already activated the button becomes "Less" and alt+m doesn't do anything further).

3) Press ALT+O to open the Format button / menu.

4. select the 'style' button from this menu
5.select the heading level from the dialogue box which appears next
6. press alt F to find next
7. press ESC to close the find dialogue box
8. use the up and down arrow keys with ctrl  to navigate between headings while in focus mode
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Regards,
Sociohack