Unfortunately, the firmware is protected by the manufacturer and is not available. With this file you will not program the processor when it is out of order and the bootloader does not work (the firmware is encrypted).
However, I know a person who had a problem (with the FY6900) and wrote to the manufacturer. They helped by selling the programmed processor and memory for the FPGA for less than $10
Damage to the power supply could lead to other damage to the electronics. Check that the processor has the correct 3.3V power supply. Unfortunately, damage to the firmware in this case is unlikely, as the processor and FPGA could be damaged (if too high voltage was applied to the electronics from a damaged power supply). To sum up, first check if the stabilizers responsible for powering the FPGA (3.3V, 2.5V, 1.2V) and the processor (3.3V) are operational.