You can't. You need the AppleID password for the account that has the device locked ... or the original purchase receipt showing you as the original purchaser (including device serial) for Apple to assist. You now have a paperweight.
I have unlocked a few icloud locked devices, and let me tell you, it ain't easy. Its not something you can just download a tool to bypass. But its not impossible lol But I don't recommend trying, since its basically just guessing the password.