On your developer pc you need to merge all 4 bin files into one .bin file. This can be achieved in two ways:
or to use github.com/vtunr/esp32_binary_merger
or to use (built-in esptool functionality, i would use this) esptool merge_bin command

On the customer pc, you may install esptool and use write_flash command, but easier way just to install Flash Download Tool from espressif tools.
Keep in mind, your start address for flashing will be 0x0000