How to Reinstall iOS 27 Using a Mac or PC

If you need to reinstall iOS 27 because the iPhone will not start normally or an update has failed, use a Mac or Windows PC for computer-based recovery. Apple recommends trying Update first when that option is available. Choose Restore only when needed because it reinstalls iOS and erases the iPhone.

Reinstall iOS from a Mac or Windows PC

Update your Mac, or install the latest Apple Devices app on a Windows PC.
Connect the iPhone with a reliable USB cable. Open Finder on a Mac or Apple Devices on Windows.
For iPhone 8 or later, quickly press Volume Up, quickly press Volume Down, then hold the Side button until the Connect to Computer screen appears.
When the computer offers Update or Restore, select Update first. Keep the iPhone connected while the software downloads and installs.

When Restore is the only option

If Update does not resolve the problem, choose Restore only after you understand the data impact. Restore reinstalls iOS and removes the data on the device. Afterward, complete iPhone setup and restore from a compatible backup if one is available.

If the download takes longer than 15 minutes, the iPhone can leave the Connect to Computer screen. Let the download finish, then put the iPhone back into recovery mode and repeat the connection step.

Before you start

Use a reliable cable and keep the computer and iPhone connected.
Do not disconnect the iPhone while an update or restore is in progress.
If recovery mode cannot update or restore the iPhone, or a required button is not working, Apple recommends seeking service.

If you want a guided desktop alternative after Apple's recovery steps do not resolve the software problem, Dr.Fone - System Repair provides an iOS system-repair workflow for software-related issues.