Interesting, as an update to the installed program should not need the installation disk.
I would suggest rebooting your system and starting TurboCAD. If it doesn't immediately prompt you to install an update, invoke the "Check for Update" menu item under the Help pull-down menu.
If prompted for the installation disk, insert it and let the update do with it as it may.
TC Pro Platinum 2020, 2019, 2018, 2017, 2016 & 2015 (all with LightWorks & RedSDK) & V21
System: i7-5820K @ 3.30GHz, ASRock X99 Extreme4, 16GB DDR4-2133 RAM, Gigabyte GTX 970, Samsung NVMe SSD 950 (256GB), Windows 7 Pro (64-bit) SP1