After Teba helps you reach Medoh and shoot its cannons to disable the force field, you can enter the Divine Beast.
Get a Treasure Chest
Turn around to face Medoh's tail. There is an eyeball on the right side of the Malice barrier. Shoot it and go to the treasure chest at the end of the tail.
Get a Second Treasure Chest
Go inside and shoot the eyeball on the right to remove the Malice barrier. Then float on the nearby updraft to the treasure chest up above on the left.
Get the Map
From the treasure chest, float down to where there is a Guardian Scout down below. Kill the Guardian, then go to the end of the hallway to find the map terminal.
Get a Third Treasure Chest
Go back the way you came and stand on the stone that is hanging from a rail. Turn right and you should see a treasure chest in the corner below. Float down to it and open it.
Get a Fourth Treasure Chest
Look down into the area below. On the left, there is a glowing eye. Shoot it, then float down and open the chest that appears.
Activate the First Terminal
Go to the updraft at the other end of this area, then float up to the chest that you opened earlier. Shoot the eyeball on the ceiling, then go through the door that the Malice goo was blocking.
Down into the room and shoot the eyeball on the ceiling on the left. Then go back up the ramp and go into your map and select the uppermost purple mark to tilt Medoh. After the tilting has stopped, float to the alcove where you shot the eyeball and you will find the first terminal.
Get a Fifth Treasure Chest
Walk onto the walkway across from the first terminal and go to the part of the walkway that is farthest from the treasure chest above the bars. From there, you can float to that treasure chest.
Activate the Second Terminal
Go down below and look for the pipe to the right of the bars. Put a round bomb into it, then detonate it to blow up the rocks that the bomb stops on.
Next, hit the crystal beside the pipe to start some wind blowing in the next room. Put another round bomb into the pipe, then when the bomb is pushed to the side, detonate it to break a rock wall. Then hit the crystal to stop the wind.
Now tilt Medoh by selecting the bottommost purple mark. Use Magnesis to put the metal ball on the track where you rolled the two bombs a moment ago. Then go back into the map and select the uppermost purple mark to tilt Medoh the other way. The metal ball will hit the plunger in the next room, opening the bars. Go into the room and activate the terminal there.
Activate the Third Terminal
Go back to the last room and hit the crystal to open the shutters in the walls. Look through the shutter behind you and you will see some of Medoh's propellors. Float onto that platform and shoot the two eyeballs in this area.
One of the eyeballs was blocking an updraft. There is a ledge near the updraft with railings on each side. Go to that ledge and look for the room in the end of Medoh's wing, between some propellors. Float into that room and activate the terminal there.
Activate the Fourth Terminal
In the map, select the bottommost purple mark to tilt Medoh the other way, then float to the central room in Medoh's body where you were before.
Go straight through the central room and you will see Medoh's other wing. Go up the short ramp and shoot the eyeball. If you are too far away, there is a ledge near the updraft to the left that puts you closer to the eyeball.
Then go back to the ramp near the entrance to the central room, and float into the room at the end of Medoh's wing. Go up the ramp in this room and activate the terminal.
Get a Sixth Treasure Chest
Go through the bars that opened, then go partly into the room and turn around. Shoot the eyeball on the ceiling near the door. A chest will fall.
Activate the Fifth Terminal
Hit the crystal switch in the room to move the battering ram against the bars. Then open the map and choose the uppermost purple mark. When Medoh is horizontal, use Magnesis to hold the sliding windmill in place. This will let the battering ram slide at full speed against the plunger. This opens the bars, giving you access to the final terminal.
Get a Seventh Treasure Chest
Go to the upper end of the the room above the crystal switch, and walk up the angled wall onto a glass window. Glide from here to the treasure chest near the sliding windmill.
Get a Ninth Treasure Chest
Float out of the open window in this room and go to the updraft outside. Use it to float on top of Medoh's head. From there, float to the treasure chest at the tip of Medoh's beak.
Activate the Main Control Unit
From Medoh's beak, float to the lower of the two updrafts and go to the top of Medoh's back. From there, you can easily reach the Main Control Unit. You will need to tilt Medoh back to horizontal. After that, check on it to begin the boss battle.