The AVB of the device can be unlocked by running the following command after booting the device into fastboot mode:
python at_auth_unlock.py cube_unlock_credentials_v2.zip
at_auth_unlock is a part of the google AVB tools and can be found here.
The AVB of the device can be relocked by running the following command after booting the device into fastboot mode:
fastboot oem at-lock-vboot!