CWM or TWRP not supported?
The "device not supported" message means that you probably downloaded the recovery image for a different device (AT&amp;T's LG G2 "d802", or International LG G2 "d800".)  You can override this check, but it's not recommended, as the devices might be different enough that you could cause irreparable damage to it (a.k.a. "bricking".) 

The most current TWRP for T-Mobile's LG G2 (d801) is located here.  I could not find an official ClockworkMod recovery for the d801, but you may want to search appropriate sections on XDA-Developers forums for unofficial builds that are compatible with your phone.  Another recovery image according to CM's installation wiki can be downloaded from here, but must be flashed with loki_flash tool, as described in the installation instructions.