Unable to install Rom on nexus 9 bootloader locked

hello guys,
I can not get into the nexus 9 because its in bootloop after 'google' logo, I want to reinstall custom ROM, I have already downloaded ROm from google website but since its bootloader is locked how do I install factory image back?



Please advice,

from xda-developers http://ift.tt/2byaJwa
via IFTTT