Cant change GO material with multipli material

when i do that it work only with the first material


but when i do that it doesnt work


how can i change my ITEM1 second material with my PE first material?

var mats = PE.gameObject.renderer.materials;
mats[0] = ITEM1.gameObject.renderer.materials1;
ITEM1.gameObject.renderer.materials = mats;

Renderer.materials** If you want to change some materials in it, get the value, change an entry and set materials back**