How can I disconnect my iCloud on my device when it is not turning on?

You can absolutely still disconnect your item from your iCloud even if it is not powered on. Please use a computer, and follow the below instructions…

iPhone Battery Issue

iPad Does Not Turn on Issue

iPhone Charging Port Issue

iPhone Power Button Issue

iPhone Boot Loop Issue

iPhone Black Screen / Does Not Turn On / Frozen Issue

Apple Pencil Battery Issue

iPad Charging Port Issue

Apple Pencil Charging Issue

Macbook Does Not Turn On Issue

iPhone Home Button Issue

AirPods Charging Port Issue

Macbook Charging Port Issue

iMac Power Port Issue