You can't. If you are referring to unlocking from the carrier/service provider, only they can do that. If you are referring to opening a phone by bypassing a lock code on the device, we cannot assist in such things. Please read the following thread... http/www.tomsguide.com/forum/id-2311806/read-passwords-lock-codes-pin-numbers.html
If it's your phone contact your carrier and tell them you found it. If it's not your phone you can't and you should turn it into the police so it can get back to its rightful owner.