If your iDevice starts acting strangely and you’ve run through the gamut of normal troubleshooting fixes, Recovery Mode may be your answer. This lets you easily reset the device and re-install iOS using iTunes.
When you reinstall iOS, there’s a chance that you may lose all the data on your phone, so it’s good to stay in the habit of making regular backups on your computer via iTunes or iCloud. With that said, here’s how you can boot your iOS device into Recovery Mode.
First, Make Sure You Have the Latest iTunes Version
First, you’ll need to make sure you’re using the latest version of iTunes. With the program open, head to iTunes > About iTunes.
Make a note of the version you’re using, and check it against this official Apple Support page to see if you’re on the newest release.
With that out of the way, you’re ready to get started. The rest of the procedure varies slightly depending on what device you’re using, so we’ll go over them one at a time.
For iPhone 7/iPhone 7 Plus or Later
If you’re using an iPhone 7, 7 Plus, 8, 8 Plus, X, XS, XS Max, or XR, here’s what to do.
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Source: How-To Geek