7 plus repair

Hi I'm new here sorry if this has been asked before. Had a 7 plus given to me to practice repairs and after replacing the screen and battery it is alive.
The laptop sees it but I can't get it to restore. I've tried updating through iTunes, ireboot etc but it gets as far as installing the firmware in recovery mode but goes no further. Literally get as far as the apple logo with the installation bar on the screen. Then once unplugged we are back to just the apple logo appearing all the time...

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