How can I unlock iPhone 6s Model A1688 from iCloud?

Activation lock is a security protocol that can't be bypassed. Only the person it is locked to can unlock it.

If you bought this from someone and it came locked, try to get your money back, you will never be able to use the phone.

If your phone is Activation Locked - How to remove Activation Lock -

How to remove Activation Lock - Apple Support

The All Too Common SAD Reality of Buying a used phone -

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

Re: “For educational purposes only! I don't have any phone to used please help to find this🥺”

If this is not your phone, you will not have this one to use, either. Read the article about “The All Too Common SAD Reality…” to get an education about Activation Lock.