How to get a Gameobject's origin to the center of it instead of the edge?

I have two different wall gameobjects. When i put both of them at 0,0,0 of the world coordinates, one of them is right in the middle (the 0,0,0 is in the middle of the wall, and it pivots around this point), but the other is left to it (the 0,0,0 is at the right edge of the gameobject, and it pivots around its own middle).

Why is that, and how can I change it? I need the second object to also have its origin/pivot point at 0,0,0 when it’s placed there.

If you made them in a modeller, go back and reset the Origin, making sure to ‘apply’ Transform. Re-export/import.

If this is not possible and you can not simply duplicate and flip the working one you can try making it the child of an empty object.