How to restore boot partition!?

Hey you guys! I was really looking for someone to possibly help me out. I actually have a G3-ls990 and have always tinkered around with any and all devices. Recently my friend ill say Mr.M9 had an update pushed to his phone, long story short first his speakers didn't work then out of no where the phone crashed and remained in bootloop. I told him I would look at it and I have. I must say DAM THIS SH#@$ TOUGHER THAN THE G3!!! MAAAAD RESPECT. I was able to get it out of booloop a couple of times by using the latest RUU then back to bootloop it went. Luckily i unlocked the bootloader on one of those lucky moments so i was even able to flash twrp and try flashing a rom. Same thing it boots up but then falls back into bootloop. I feel like the boot partition has been corrupted in a way. I would like to restore the factory boot image, but how is that even possible for the sprint htc one??? thanks in advance

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