How can I log them out from my phone

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 iPad/iPhone.

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

Assuming you are not the original owner, hence the question. The previous owner should follow these steps: What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support