Iphone firmware help

My son as done a update on his iphone 8, after update it went into loop mode, just getting to the apple logo then rebooting, tried alsorts to fix it, eventually done a factory reset, worked for a hour then back to the same. Does anyone know any of these ISO firmware fixer apps that are actually free?? Downloaded a few, it then downloads the firmware then asks me to pay to fix it, I have used a free one before what worked but I cant remember the name of it. Thans