Note that your NVDA key will be either INSERT or CAPS LOCK, depending on what you have setup. As Gene suggested, if you can't get to it that way, you can go via the notification area (system tray):
1. Press WINDOWS+B to jump to the navigation area.
2. Press the RIGHT ARROW to move to the NVDA icon (If you can't find it, go to "Notification overflow chevron", enter on that and then arrow through the extra icons).
3. Press ENTER to open the NVDA menu
4. Press DOWN ARROW once to "Preferences"
5. Press ENTER to open the sub-menu
6. Press ENTER again to open "Settings".
7. Press CONTROL+TAB to get to the "Keyboard" settings.
The first option is the Keyboard Layout. Basically Desktop layout uses the number pad for some functions, and laptop layout doesn't. So if you want to use NVDA+DOWN ARROW to say all from the current point, then you want Desktop Layout. If you want to use NVDA+A for Say all, then that's Laptop keyboard layout.
The next option is your NVDA modifier key(s). You can select one or more of:
INSERT (The one near DELETE, HOME, END, PAGE UP, PAGE DOWN, etc)