You have to run "install product code" on the calculator to go to the boot code.
Then on ti connect, run "Tools \ Ti Os Downloader" and follow the process page 43 of https://education.ti.com/en/guidebook/details/en/2AEC20243FBD4F02A2B63F5B19955A78/ti-connect
(Your calculator may appear non connected, but the os downloader should still work).