Remap Quick Split

[QuillianInkheart]

I'll preface with the fact that I'm using a Switch controller for this. I did a basic remap to switch A and B in the menus, but ran into another problem almost instantly. For some reason, the game has mapped the inventory's quick split and quick transfer to the same button (X), so now I can't pick up a full item stack and swap it quickly, but always a half-stack. This has made quick transfer utterly useless, since it now takes twice as long to quick transfer as it does to just pick up a stack and manually adjust the page.

How do I remap Quick Split so it isn't set to such an obnoxious position?