Pixhawk4 showing secure bootloader but firmware not getting booted in QGC

I have securely signed a Pixhawk4, it is showing that the bootloader is secure when I use dmesg command but it is not getting booted when connected to QGroundControl or any other GCS or there is no option to flash the bootloader again. It seems the issue is with the Pixhawk. Can you help me in identifying this issue or provide a method to reset the whole device? We have around 3-4 Pixhawk devices with the same issue. Thanks in advance.

Use STM32 ST-Link utility and USB ST-Link to reflash the whole device and reinstall the bootloader