I have buy second hand iphone but owner also not remember apple id or password my phone show activation lock after reset so what can i do . Please help me

Given what you say, your only possibility for getting the activation locked removed is for the prior owner to have their purchase receipt for the device from an authorized Apple seller with the device’s serial number on it. If they have it, then they may be able to persuade Apple support to remove the activation lock. Have them use support options below to persuade Apple support. Alternatively, if an Apple Store is open in their area, they can go there to deal with the problem. In this case, they can make a genius-bar appointment (https://www.apple.com/retail/geniusbar/) if desired.

Apple ID Support https://support.apple.com/apple-id

Apple Support Twitterhttps://twitter.com/AppleSupport

Apple ID account security for country-specific andregion-specific help https://support.apple.com/en-us/HT204169

Get Support: We’re here to help https://getsupport.apple.com/. Go through the options to find the best support option.

See if they can recover the ID/password.

Apple ID - How to find your Apple    An iCloud e-mail address is an Apple ID.

Apple ID - Find              

Enter the Apple (iCloud) ID and click Forgot Password.

Apple ID - Manage            

Apple ID – Forgot Password            

You will need the Apple ID and password to unlock it. Otherwise the phone is useless.