I currently have an iPhone 4 running on iOS 4.21
The phone is currently on baseband 2.10 jailbroken and unlocked with geveySIM on Tmobile network
The phone runs fine and I'm just restoring the iOS 4.21 to recalibrate my proximity sensor since I recently replaced it and was told to restore the iOS software to recalibrate the sensor.
I have made backups of my contacts,playlist, and apps.

Can someone please tell me what do I have to download and list the sequential steps in order to restore the phone to iOS 4.21.
(the saved ssh I have on the phone are 4.21)