Hey there, you need to have done enough of Micah-10's 'Alone in the Dark' missions to unlock the Blooming's Cyst missions, that's where the collectible is. If the Blooming is set to the Slayer cyst, you have to enter through the Fallen area with the glowing blue floor, just after leaving the Blooming, and finish the Cyst encounter to access the collectible. But if you set it to Searing Light, that's the one with the waterfall entrance and allows access to the collectible immediately after dropping the Hive barrier.