It is likely that moving the left 'OK' button to the area of the right window will be problematic due to graphics issues, the overall inelegant design of the window, and confusion when using these buttons.

Then, perhaps, both buttons could be moved to the border between the windows, i.e., the left button to the right corner of the left panel, and the right button to the left corner of the right panel. The main thing is that the buttons should be close to each other; this will prevent people from forgetting that there are two buttons. I don't think there will be any confusion; people will get used to it.

If there is a redesign, there will be no getting used to it; it is deeply ingrained.

The problem is that the appearance is still the same (in the usual place, in the right corner, there is one familiar button), but the function has changed – it focuses on the right hero, not the left, as everyone is used to. To get used to the new function faster, the appearance needs to be changed; as an option, put 2 buttons next to each other; this will remind people that the function of the right button has changed and will reduce confusion.