How do I unlink two planes?

Development Getting Started & Setup
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Hi there, I've built this room by making instances of planes and used "Break instances" in an attempt to make it possible to apply individual textures to the planes. It works for some planes, but here this scaled up texture is applied without the scaling attribute to other planes too and I can't figure out how to unlink them. Do you have an idea? Should I just delete affected planes and rebuild?

The tiny thing next to the door is this same texture. Would like to be able to put another texture on the plane next to the door.
The tiny thing next to the door is this same texture. Would like to be able to put another texture on the plane next to the door.720×449 87.8 KB