From what I understand, the likes of Fallen Aasimar etc have been scrapped for Variant Aasimar and Celestial Revelation.
Where abouts is Celestial Revelation option supposed to show up in the character creation? When I select my character to Level 3 I can't see any option for it in any menu. Is it locked behind a sourcebook?
Variant Aasimar is the term for the version of the aasimar that was published in the DMG as an example of creating your own races. The first "real" aasimar, with subracees, was published in Volo's Guide To Monsters, which is now Legacy content.
Both the Variant and the version with subraces are in the character builder under the same heading.
The aasimar you're thinking of (with the level 3 options to choose) is the one published in Morden-whatever's Monsters of the Multiverse. It's a separate entry in the character builder. (See attached screenshot) If you want that one specifically, make sure you have access to the new content (either from owning Monsters of the Multiverse or from having purchased the new aasimar individually), and make sure you're looking at the correct "Aasimar" in the character builder. If you see "Fallen," etc. as selectable subraces, you're on the wrong one.
ETA: Just to be doubly clear, "Variant" is not the one you're looking for.
From what I understand, the likes of Fallen Aasimar etc have been scrapped for Variant Aasimar and Celestial Revelation.
Where abouts is Celestial Revelation option supposed to show up in the character creation? When I select my character to Level 3 I can't see any option for it in any menu. Is it locked behind a sourcebook?
Variant Aasimar is the term for the version of the aasimar that was published in the DMG as an example of creating your own races. The first "real" aasimar, with subracees, was published in Volo's Guide To Monsters, which is now Legacy content.

Both the Variant and the version with subraces are in the character builder under the same heading.
The aasimar you're thinking of (with the level 3 options to choose) is the one published in Morden-whatever's Monsters of the Multiverse. It's a separate entry in the character builder. (See attached screenshot) If you want that one specifically, make sure you have access to the new content (either from owning Monsters of the Multiverse or from having purchased the new aasimar individually), and make sure you're looking at the correct "Aasimar" in the character builder. If you see "Fallen," etc. as selectable subraces, you're on the wrong one.
ETA: Just to be doubly clear, "Variant" is not the one you're looking for.