To reset admin password:

Method 1 - reset admin password directly in database:

mysql> SET @salt = MD5(UNIX_TIMESTAMP());
mysql> UPDATE admin_user SET password = CONCAT(SHA2(CONCAT(@salt, 'MyNewPassword'), 256), ':', @salt, ':1') WHERE username = 'admin';

Method 2 - using PHP to generate the password. Then, reset it in database:

# php -r '$salt = md5(time()); echo hash("sha256", $salt . $argv[1]).":$salt:1\n";' MyNewPassword

66bdd4e5008cad465a6cd23eb6ac3aa6ef4c65d07a179157bab11935f9f4d62f:a4506164831ba6f12474a3ffe57602d0:1

mysql> UPDATE admin_user SET password = '<code above>' WHERE username='admin';

Method 3 - Generating the password. Then, reset it in database:

Add the following line at the last line and loot at the footer of any page.

# vim pub/index.php

echo \Magento\Framework\App\ObjectManager::getInstance()->get("\Magento\Framework\Encryption\Encryptor")->getHash("MyNewPassword");

Method 4 - Create a new admin user. Then, reset the previous admin password:

# php bin/magento admin:user:create --admin-user=admin2 --admin-password=MyNewPassword2 --admin-email=admin@example.com --admin-firstname=admin --admin-lastname=admin

Reference:

http://magento.stackexchange.com/questions/90922/how-to-reset-lost-admin-password-in-magento-2/161792#161792