The new version may have contained flaws that caused your device to lose a lot of battery while also preventing the boot-up process from finishing. Forcing your iPhone to restart while charging might be able to help in this scenario. As a result, here's what you should do:

1. Connect your iPhone to a power source and charge it for around 20 minutes using the original (Apple-supplied) charger. It should be plenty of time for your gadget to charge up.
2. Force restart your iPhone 7 once the timer has expired by pushing and holding the Sleep/Wake (Power) and Volume Down buttons for around 20 seconds or until the Apple logo shows.

I hope this solves your query

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