Hi Zhitai Liu,
Thank you for your interest in NXP Kinetis product, I would like to provide service for you.
From the KV10Z reference manual, you can get that the FSEC is in the flash address 0x40c.

The FSEC bit meaning can be found in the register:

If you want to change the SEC bits, you can modify it in your code project.
Now, take MDK project as an example:

Change the FSEC is OK.
Wish it helps you!
If you still have question, please let me know!
Have a great day,
Kerry
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