You can't. According to the inquiry of official website, Shenzhen Municipal Government, the qualification certificate for law enforcement of fire professional examination is as follows.

1, staff of administrative law enforcement organs or authorized organizations.

2. At least 18 years old, with high school education or above.

3. No criminal punishment or administrative sanction of dismissal from public office.

4. After resigning as a fireman, you can take the law enforcement certificate. Therefore, Shenzhen fire experts can't take the law enforcement qualification certificate.