if you buy a icloud lock logic board and installed it in a iphone shell. How do you remove the icloud lock?

You cannot. There is no way to legitimately remove Activation Lock without the Apple ID and password used to lock it rod original proof of purchase from Apple air an authorized reseller. It's an anti-theft feature. it is designed precisely to stop others from using stolen or lost iPhones.

Without the original user's Apple ID and Password there is no way to remove it. Sorry. That "logic board" can never be used again.

If you replaced it for one that is not iCloud Locked yes. Same as just finding an iPhone that is not iCloud locked. Good luck finding a real unlocked logic board in the secondary market.

There's a reason they are sold as parts rather than complete iPhones.

What if you replace the logic board? Will that allow you to use the phone?