Lens calibration is for advanced user's like yourself, and is initially disabled to prevent novices from stumbling into it.
If you look at the GBTEOS User's Guide and search for calibration, you will find this ...
The lens calibration settings are enabled only to “Super Users” who wish to calibrate their own lens. See Appendix E for instructions on calibrating a lens.
If you search for super user you will see that it is an option in the Tools/Options