Current TDC-3 firmware is v3.26 (January 2022).
To update the TDC-3, select Menu-> System-> Program-> Update Chk. Logon to a Wifi, or tether through your phone, and get the latest firmware versions automatically.

Download the TDC-3 user manual. 

Download the TDC-3 Dive Log manager: Windows 32/64, or Mac OSX / MacOS