How do I remove iCloud from my Apple device?

Not sure exactly what you think you intend to accomplish, but you can sign your devices out of iCloud as described here:

Sign out of your Apple Account and iCloud on your devices - Apple Support

Perhaps if you shared your concerns we might help w/ a less-drastic solution.

From your title I am going to guess you may mean this:

If you see a "Locked To Owner" message or one referring to Activation Locked (iCloud locked), read this Activation Lock removal article --> How to remove Activation Lock - Apple Support To remove the lock you will need either:

-The account information that set the lock (if the previous owner is deceased, read —> Request access to a deceased family member’s Apple Account - Apple Support )

OR

-The original sales receipt from Apple itself or an Apple approved vendor. Other ways you may think might be “proof” of ownership or purchase, such as having the box, or a receipt from a third party vendor such as Ebay, will likely not be acceptable by Apple. Apple may have no way of verifying the authenticity of other methods. If you have an acceptable receipt, ask Apple to unlock the device —> https://al-support.apple.com/#/additional-support

If anybody tells you that you have to be the “original” owner, they are incorrect. As long as you have the original Apple receipt (which may well not have any personally identifying information on it) you are okay.

If it is asking for an account that is not yours, take it back to the person from whom you received it. Get them to do the things in this support article or ask for a refund --> What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support There is no way to discover the owner of a device unless they left a message to display on the device when it is turned on, or the person who gave you the device knows them. Note that the device cannot have Lost Mode set on it. If your device has been taken over as a result of you having entered a scammer’s Account then the scammer may have set Lost Mode too and the device is lost to you.

Return or recycle the device if you cannot unlock it; it is useless to you. From the very bottom of Apple Trade In - Apple :

"Does Apple offer recycling?

Yes. Apple Trade In lets you recycle any Apple device (including devices from Apple-owned brands) at any Apple Store and on Apple for free. That includes your batteries and old electronic products as well as free, on-demand packaging recycling for our commercial, education, and institutional customers. When we receive your device, it will be thoroughly inspected to determine if components can be recycled or reused. Whether recycled or reused, all activities relating to the processing of your device will be managed in an environmentally responsible way."

When considering future purchases read these:

The All Too Common SAD Reality of Buying … - Apple Community

If you want to buy a preowned iPhone - Apple Support

I honestly don't know what you mean when you say "BIU". Please tell us which of these definitions for "BIU" you are using and how they apply to your issue:

Bold, Italic, Underline (font)

Bar Ilan University (Israel)

Bus Interface Unit

Bundesverband Interaktive Unterhaltungssoftware (German)

Bibliothèque Interuniversitaire

Blaze It Up (band)

Bulk Import Utility (various locations)

Basic Information Unit

Bircham International University

BikeTrial International Union

Beach Interface Unit (US DoD)

Business Intelligence Unit (market data analysis)

Billion International Units

Basic Income Unit

British Independent Utilities (UK)

Buffer Interface Unit

Bildudalur Airport (Iceland)

Brothers in Unity (band)

Blow It Up

Background Investigation Unit (Colorado Department of Human Services)

Benson Idahosa University

Basic Interface Unit

Baseband Interface Unit

Bangladesh Islami University

Business Insurance Underwriters (Wheaton, IL)

Burnett International University (Haiti)

Beat It Up

Beirut Islamic University

Broadcasting for International Understanding (French)

Built-In Unit

Business Interruption Unit

Bureau d'Inscription Universitaire (French: University Enrollment Office)

Boundary Intersystem Unit

Belarusian Insurance Union

Biomedicum Imaging Unit

Blantyre International University (Malawi)

Berkeley International University (Delaware)

Business Ideas Unlimited (Australia)

Barrier Industrial Unions