This does not downgrade the system firmware. It only restores the user data partition. The core iOS remains the same.
If prompted, you will also need to import your saved SHSH blobs to verify the firmware. how to restore unsigned ipsw with 3utools
Download and install the latest version from the 3uTools official site. Step-by-Step Guide to Restore Using 3uTools
If you want to restore unsigned firmware, you need to understand (Signature HaSH). This does not downgrade the system firmware
Select the SHSH2 blob file that corresponds exactly to the firmware version you are trying to restore. Put Device into DFU Mode Follow the on-screen instructions in 3uTools to enter
3uTools will attempt to verify the IPSW signature. Since it’s unsigned, the baseband and kernel flash will fail. However, the tool will then try to mount the user partition and restore only your data to the existing signed firmware. If prompted, you will also need to import
Click and select the unsigned IPSW file you downloaded.