Since you did not specify which specific tool you are looking for (there are several major ones), I have provided the official or verified download sources for the three most reputable tools in the industry, followed by a solid review of each.
Let’s assume you have obtained a legitimate IPSW download link and downloaded the file. Here is the exact procedure. iphone firmware flash tool link
Because macOS and Windows handle these tools differently, this guide covers both official methods and third-party tools. Since you did not specify which specific tool
If your device is stuck on the Apple logo or in a recovery loop, ReiBoot is the leading specialized repair tool. It offers a "Standard Repair" mode that can flash your firmware without data loss, which is a significant advantage over traditional methods. Because macOS and Windows handle these tools differently,
Signed Firmware: Apple only allows the installation of "signed" firmware. Attempting to flash an unsigned (usually older) version will result in an error.
Alternatively, you can also download the tool from other reliable sources, such as: