Is there a way to regenerate attraction?

Hmm... I tried my best to understand it...

Have you tried setting them in CAS? It's simple: just open the Simology panel (the place where the traits and aging bar are), scroll down until you reach likes and dislikes section, and in there there's a button to edit them in CAS. Turn-ons and turn-offs can be changed there.

Or did the other teens not in the rotation generate these? In this case, go to Manage Worlds, open Manage Households panel (top right button), and find those teens. Once you found the household they're in, click on them, then you can edit them in CAS.

No no, as in

• I loaded in the game.
• The teens instantly decided they hated each other attraction wise (before either of them even had opinions on what they like and don't like)
• I go into CAS
• Choose what their attracted to. I make sure it all fits the other sim perfectly
• I leave CAS
• They still hate each other. No other opinion they'd developed changed.
• Any new sims they meet now base their attraction off what I've selected, but any sim they met before isn't able to be changed.

I'm asking if there is a way to fix this so that they decide if they like each other based on what I've picked instead. Like to reset what they think of each other.

There is no physical attraction in game, just compatibility based on likes, dislikes, turn ons and turn offs and traits. You can edit likes and dislikes, turn ons and turn offs, but there is nothing you can do about how the traits interact with each other to create compatibility between the sims. Maybe you could change traits or go to counselling classes and work on the relationship, but my understanding is that as long as the romance bar is full they are a solid couple. 

Is the romance bar red? Do they have negative sentiments towards each other? If that's the case, then nothing but time and treating each other better in game will fix it. If one has a major negative sentiment it either has to decay over time or be replaced with another equally powerful positive sentiment.

If you still want them to be soulmates, you may need to play out an enemies to lovers story with them.

If that's not it, then I don't know what's wrong. It may be a bug in game.

Have them interact again. My sims start out neutral towards each other even after I assign turn-ons and turn-offs, but as soon as they interact, it should change.

Have they asked each other about attraction since you changed the TOTOs? That should have them review their opinion on a sim based on their TOTOs and everything they know about the other sim. 

It's an interaction under the new social category.

I'm having the same problem, when they ask to the other they say that "I never thought much about it" (implying that they have no preferences for anything). But I did assign the turn on & offs, it work with sims that they didn't know before, but for the previus relationships from before this update don't work

The first thing that comes to my mind, is to take the separate families into your My Library. This will break any relationship between the two families. (This normally works, at least prior to Lovestruck.) But it's worth a try. Best of luck. This sounds like a terribly frustrating situation for you.

Do you have mods? If not turn off attraction and turn it off to see if it works. This could be a bug. 

Delete the sim and reload !