Hi,
The LPC4353 has on-chip flash, I suppose that you have to program your application code to the flash.
If you have the source code project, you can use keil, IAR or MCUXPresso tools to download the code.
If you has the *.bin or S_record file, you can use FlashMagic tools to download the code in ISP mode.
https://www.flashmagictool.com/download.html&d=flashmagic
Hope it can help you
BR
XiangJun Rong