Sadly, you can't do anything.
The system sadly (client) is set the way it is with no ticking/unticking option for the shield slot:
Whatever IM shield you put on will cover the regular one automatically (yes, this even includes the stupid new origin bracelet). Switching view for the shield objects on and off is not possible, there is sadly no option programmed in.
The moment you put off whatever IM shield "object" is sitting on the IM shield slot, the real one becomes visible- automatically. As soon as you put anything on the IM shield slot, it gets covered with whatever you put at that slot (even "invisible" objects like the new origin bracelet) - this happens automatically too.
This view change is programmed in the client, it gets automatically triggered (for each class btw) as soon as you put any IM item on that is placed on the shield slot. Since the knight class is the only class in the game that has any visible shield objects (and the warrior base class), the knight is sadly the only class in the game that is facing this issue. All other classes do only come with invisible equip and IM shields, so there was no need for any ticking option for about 95% of the classes. (I don't say I like this) Sadly me thinks the Korean Devs didn't think about the knight class and the warrior base class and it's shield items. They simply forgot me thinks.
And so we knights have to live with either nothing put in the IM shield slot to make our gear visible, or to live with any other visible IM shield that sits on the slot - in the case of the zodiac. Or with simply no shield shown at all in the case of the new origin bracelet.
You basically have only two options: to live with the look of the zodiac shield, or to live without any IM shield equipped at all.
In my personal case I made the decision to go without any shown shield object at all, cause I for myself found wearing the new origin bracelet more important than a shown shield.....just telling to let you know I face the same issue and I learned to live with it.
I doubt that Warpportal will be able to fix this at the moment. And I doubt they will be able to fix this in the near future too. I truly think this kind of bug is a tough one and lies deeply in the code. You really need to have deep insight in the codings to even be able to find the code causing this. And fixing it is another thing.....