you guys need to first meet that deoxys guy in the town that has the passage to the victory road he will be in that cave south west
You have to find the Hiking boots I think they replaced Rock Climb for hiking boots
After leaving the vulcano-area, back in Deyraan Town stand between the lower entrance and the waterfall-pond and use heart-swap on the manaphy-statue above the waterfall.
through the cave and outside at the base of the mountain make your way to Narra Town.
Try to leave the town to the south to activate a talking-scene.
After this, head back to the darkray-base and the staircase is back in place at the position of OverHeavenās screenshot.