Here’s how to activate the Heroic version of the Rift Generator public event in the Dreaming City in Destiny 2 Forsaken.
The Rift Generator will spawn and you have to initiate the boot sequence where a wave of enemies will spawn in front of you, including a Deranged Abomination.
When you kill him, he will drop an orb. Pick this up and deposit it into the Rift Generator to begin the sequence. You will have to defend the generator core during this event and should its core integrity begin to drop you can deposit orbs from further Abominations you defeat to bring it back up to full.
Defending it until the timer runs out it is how you would complete this event normally, but if you want to turn it into a Heroic event you will have to defeat Fallen Blights that spawn ahead and either side of you. Shoot them until they are destroyed or sink into the ground as and when they appear.
Once you’ve killed a bunch of them, a Blight will appear above the Rift Generator and three Taken Wizards will spawn. After killing them you will be teleported into the Ascendant Realm where the Heroic Event is triggered.
Defeat the waves of enemies and the boss to complete the event. Many of the enemies have roughly 540 power so it might be an idea to do this as a team and share the loot with your friends.