Making a few assumptions here, your attempting to flash your ESCs with BLHeli Suite, you've probably tried numerous ways 1-wire interfaces, CleanFlight pass through and still can't connect to the ESC. It very probable the ESC has no bootloader flashed on it.
In the case there is no bootloader you will need to flash the SimonK or BLHeli bootloader (BLHeli bootloader is smaller in size).
Easy option: For an ESC with ATMEL chip you can use a flasher tool to directly flash the firmware to the chip. Example, ZTW Spider 12A ESC's may or may not have a bootloader flashed:
Expert option: Another alternative that requires soldering wires to the chip and an USBASP programmer refer to http://dronesdecarreras.com/tutorial-como-flashear-tus-esc-atmel-con-blheli/ (translate to English).
Other useful references: