About error 53
After you try to update or restore your iOS device in iTunes on your
Mac or PC, you might see error 53 in iTunes and "Connect to iTunes" on
your device. Error 53 appears when a device fails a security test. This
test was designed to check whether Touch ID works properly before the
device leaves the factory, and wasn’t intended to affect customers.
For anyone who experienced error 53, Apple has released an update to
iOS 9.2.1 to allow you to successfully restore your device using iTunes
on your Mac or PC. Use the steps in this article to restore and recover
your device. If you believe that you paid for an out-of-warranty device
replacement based on an error 53 issue, contact
Apple Support to ask about reimbursement.
Source :
https://support.apple.com/en-au/HT205628
Link Download New IPSW 9.2.1