Activation of iCloud

If your iPhone has an Activation Lock on it then you will need the Apple ID and Password of the previous user to unlock it. There is no other way to do it. You will not be able to use the iPhone if you are not able to remove the Activation Lock.

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If you are the owner of the iPhone or the owner has shared all information with you then to open Activation Lock:- If it is Activation locked, read here --> Turn off Activation Lock - Apple Support Activation Lock for iPhone, iPad, and iPod touch - Apple Support

Learn how to remove a device from a previous owner's account.

If you are not the owner of the iPhone and do not have the Apple ID and Password then there is no way that you can get into this iPhone unless the original owner shares the Apple ID and password with you. If you are lucky you can get into this iPhone if they (owner) accidentally remove the device from their apple ID.