OTA Downgrade refers to the process of restoring devices to an "OTA signed" version. These versions are being signed by Apple, making downgrades possible, but it cannot be done through iTunes. Legacy iOS Kit can do this procedure for users as long as they fulfill the requirements.
The three versions that are "OTA signed" are iOS 6.1.3, 8.4.1, and 10.3.3. However, the versions supported for each device vary, see the table below for details.
Requirements
| Target Version |
Supported Devices |
| iOS 10.3.3 |
A7 devices: |
| iPhone 5S |
| iPad Air 1 |
| iPad mini 2 (except iPad4,6) |
| iOS 8.4.1 |
32-bit devices: |
| iPhone 4S |
| iPhone 5 |
| iPad 2, iPad 3, iPad 4 |
| iPad mini 1 |
| iPod touch 5 |
| iOS 6.1.3 |
iPhone 4S |
| iPad 2 (except iPad2,4) |
Usage
For usage, go to Restore 32-bit device or Restore A7 device to iOS 10.3.3