After activating the Main Control Unit of Divine Beast Vah Rudania, you must battle Fireblight Ganon.

First Phase

Stay near the Main Control Unit to avoid falling off into the volcano.

Fireblight Ganon will attack with its sword. Watch for when Fireblight Ganon pulls the sword back before striking, and try to backflip or jump to the side to avoid these attacks. If you do a Perfect Dodge, you can hit Fireblight Ganon with a Flurry Rush.

If Fireblight Ganon throws fireballs from his hand, run or jump away from them.

You can also shoot Fireblight Ganon in the eye to stun him.

Second Phase

When you have reduced Fireblight Ganon's health below 50%, his attack pattern changes.

He will start putting a force field around himself while charging up a large fireball. Use an ice arrow to freeze the fireball, or hide behind an obstacle to avoid the fireball's explosion on impact.

When you see Fireblight Ganon pulling in energy to charge up the fireball, throw a bomb at him and detonate it when it is close. He will be stunned, giving you time to attack.

During this Phase, Fireblight Ganon may also aim at you with a red laser before shooting an energy blast at you. If you can, try to use your shield to do a Perfect Guard and knock the energy back at Ganon. He will be stunned, so you can run in and attack.

After

Get the Heart Container, then activate the Main Control Unit. The game will tell you that you can't re-enter Vah Rudania after you activate the Main Control Unit, so explore the dungeon now if you want to. You can take a picture of a treasure chest to add it to your Compendium, then use the Sheikah Sensor to find any treasure chests that you might have missed.

After you activate the Main Control Unit, you get Daruk's Protection. Hold ZL to activate the force field. You can disable Daruk's Protection in your inventory in the Key Items section.

Go into Goron City and there will be a cutscene. Go talk to Bludo to complete the Divine Beast Vah Rudania quest, then go into Bludo's house to get the treasure that he mentioned. It's on Bludo's throne.