Use iTunes (Windows/macOS) with a computer you trust
Connect iPhone to the computer with a USB cable
Open iTunes (or Finder on macOS)
Put iPhone into Recovery Mode
iPhone 8 or later: Press and quickly release Volume Up, press and quickly release Volume Down, then press and hold Side button until Recovery Mode screen appears
iPhone 7 / 7 Plus: Press and hold Volume Down and Side button until Recovery Mode screen appears
iPhone 6s or earlier: Press and hold Home and Side (Top) button until Recovery Mode screen appears
When prompted in iTunes/Finder, choose Restore
Wait for the restore to complete
Set up the iPhone after it restarts
Use macOS Finder (if applicable)
Connect iPhone to Mac
Open Finder
Select the iPhone in the sidebar
Put iPhone into Recovery Mode
Choose Restore when prompted
Wait for completion
Use iCloud Erase (only if Find My iPhone is enabled and you know your Apple ID password)
Go to iCloud.com on a computer or another device
Sign in with your Apple ID credentials
Select Find My
Select your iPhone
Choose Erase iPhone
Confirm to start erasing
If you do not know the Apple ID password and Find My iPhone is enabled
Use Recovery Mode + Restore (may still require Apple ID/verification after restore)
Contact Apple Support or visit an Apple Store for account recovery options
If you have an admin-managed/work/school iPhone
Contact your organization’s IT administrator for device reset/unlock procedures