Hold down the Option (Alt) key and click Restore iPhone . Windows: Hold down the Shift key and click Restore iPhone . Browse and select the .ipsw file you downloaded in Step 1.
"Flashing" an iPhone refers to reinstalling its operating system (iOS) using firmware files known as . This process is often used to fix severe software glitches, repair a "boot loop" (where the phone is stuck on the Apple logo), or perform a clean install. iphone firmware flash tool link
Flashing firmware does not bypass iCloud Activation Lock. You must know the Apple ID and password originally linked to the device to set it up after flashing. Hold down the Option (Alt) key and click Restore iPhone