Can i unpatch a ISO?

look i have this JAK X pal iso i patched to ntsc...

now it wont boot.

anyway to unpatch it ...?

I don't heard about un-patcher apps

PPF patches can contain undo data in theory, but it's up to the patch maker whether they do or not.

I can't really tell you how to check for it; instructions probably came with the patcher. I haven't installed a PPF since my days hacking the PSX. (I used to do a lot of PAL2NTSC and Modchip detection skips, but nowadays a DMS4 chip will do both on its own!)