I don't believe you can. Once you create a custom unlock, you cannot fly outside of it, once inside of it. The rest of the world outside the custom unlock becomes an NFZ. That's why custom unlocks should be avoided wherever possible.
However...
From a Drone savy member of the forum named GadgetGuy from an post long ago.......This just may be whats happening
""You have to be inside the unlock when you launch, because the area outside the unlock automatically becomes an NFZ. If you...
1. I’m not sure what the question is? You werent prevented from flying right?
2. DJI has mostly ended forced no fly zones. Positively verify that DJI still has forced no fly zones in your country.
3. Notices in the app may seem scary but they...
I think this is a fair question.
I never update quickly; I am queasy about being the beta tester on things that DON'T fly.
So, I'd simply hold off when an update comes out. The early-adopting canaries will let you know if the last update is a...