Messed up Deal With The Bandits quest

I went through this quest with the intention of helping out Oak. I obtained the two amulets and returned to Oak. By accident, I clicked the option to kill Oak (sorry Oak!). Before he died, I quit the game. I logged back in and Oak was there. This time I talked with him and selected to help Oak. I was awarded with "The Apex". I had no idea what to do with it. Looking online, it says to return it to Eramir. However, I don't have a quest for that, and he doesn't seem to want it. How do I fix this?

the apex activates the act 2 boss. (vaal oversoul) its in in the ancient pyramid after the caverns

Just progress in the game.

You will acquire the Apex regardless if you help Eramir or one of the Bandits, and the story won't let you proceed further until you will make your choice between Eramir or the Bandits (the game will let you know when by not allowing you to reach the last zone of Act 2 until you choose).

After you have the Apex, simply proceed to the end of Act 2. You will reach an Arena, where you need to socket the Apex in an altar. After that, get ready for an obvious boss fight with the Act Boss for Act 2.

Do remember that your bandit choice (or your choice to help Eramir) is not fixed. You can still use a Recipe to get a Book of Reform that will let you change your Bandit Choice, by vendoring 20 Orbs of Regret and an appopriate Amulet depending on what Bandit's Favour you want to get: Amber for Oak, Lapis for Alira, Jade for Kraytin, Onyx for Eramir.
Be careful, however, that if you chose to side with Eramir and want to swap for another Bandit you must have 2 Unallocated Passive Points in order to read the Book of Reform, since you will inevitabily lose them.