The entrance to Cauldron RHO can be found by climbing down the trench. Just follow the path down and you should find the entrance.
Override the door and enter the Cauldron. Explore around and navigate your way to the Blaze Processing Chamber. You will have to make use of the moving platforms and rotating gears to get around and through the Blaze Processing Chamber.
Similar to Cauldron SIGMA, you must find the cauldron core and override it which will result in a boss fight.
Once you've gotten through the sealed chamber, use the gears to get to the other side. Make a left and continue down that path until you find an override bridge. Cross the bridged, continue on the path and you should be climbing down into the entrance of the cauldron core.
You'll be going up against two medium sized machines this time. A Snapmaw and a Ravager. You can set up several traps around the area before the fight starts. Both machines stand close to the ground and can easily be destroyed with blast traps. You can also choose to tie down one of the machines with a ropecaster and take on the other machine in a one on one scenario.
Once you've killed both machines, override the core to gain access to override data and complete the quest.
