If you've screwed up the LDO/SMPS and/or VOS settings it will brick the board.
The recovery method in that case is to solder a link on the BOOT0 pin so it is high. Then cycle the board power completely (remove all connections/power sources) several times, until you can connect.
Check you can connect with STM32 Cube Programmer or ST-LINK Utilities, and then Mass Erase your code from flash.
On the H747I-DISCO I had, access to BOOT0 was via a small resistor pad (R192) under the screen. You'll need to check docs for current board to confirm.
Then, once recovered, stop putting code with broken settings on it, or provide secondary methods to stop the clock/system configuration code running.