How can I activate my iphone without previous owner

You will need the cooperation of the previous owner who set the Activation Lock, a theft prevention feature.. Without the Apple ID and Password of the original owner, you will never be able to use the device. Check these links...

Turn off Activation Lock - Apple Support

Activation Lock for iPhone, iPad, and iPod touch - Apple Support

If it is asking for their Apple ID and password, you can’t use it without their help. If you can’t contact them, recycle it and buy a phone you can use.