I had received an RMA's tablet years ago and never rooted or unlocked the new one since I had no need. I'm giving this away and wanted to customize, but found the device unlock tool V6 was not working (device not supported error).
I'm going to describe how I unlocked and installed TWRP for future reference.
Step 1: (taken from TWRP site
Fastboot Install Method (No Root Required):
You will need the platform-tools from the Android SDK on your computer. Find the SDK Only section on the page linked and install the SDK and download only the platform-tools to get adb and fastboot binaries.
Windows users will need proper drivers installed on your computer. You can try the Naked ADB drivers or the Universal ADB drivers if you don't already have a working driver installed
On your device, go into Settings -> About and find the Build Number and tap on it 7 times to enable developer settings. Press back and go into Developer Options and enable USB debugging. From your computer, open a command prompt and type:
adb reboot bootloader
Step 2: (taken from this forum
fastboot erase system
fastboot erase recovery
fastboot erase userdata
fastboot erase boot
fastboot erase misc
fastboot erase cache
fastboot -i 0x0B05 flash staging twrp.blob --------- location of twrp blob !!!!!
fastboot -i 0x0B05 flash recovery twrp.img --------- location of twrp blob !!!!!
Step 3: (taken from this forum
adb devices [device should detect in recovery mode]
adb shell [after this command yu should see "#"]
Next run these cmmds 1 by 1
dd if=/dev/zero of=/dev/block/mmcblk0p4 bs=100 count=1
dd if=/dev/zero of=/dev/block/mmcblk0p3 bs=16 count=1
Step 4: (taken from this site
adb push rom.zip /sdcard/