Zen-Cart troubleshooting – if you had lost the password, one of the most direct ways is to use the reset password function, which would send you the instruction to the admin e-mail.  Yet, the e-mail function may not work or the email address cannot be recalled.  In such case, one can use the PHPMyAdmin commonly found in CPanel to reset password directly (credit: inmotionhosting).

Here is the SQL instruction to reset it (tested on zen-cart 1.5.4 myself)

DELETE FROM admin WHERE admin_name = 'Admin'; 
INSERT INTO admin (admin_name, admin_email, admin_pass, admin_profile) 
VALUES ('Admin', 'admin@localhost', '351683ea4e19efe34874b501fdbf9792:9b', 1);

The logins/password will be Admin.  Definitely you should immediately change the password afterward!

Credit Source: https://www.inmotionhosting.com/support/website/zen-cart/resetting-your-zencart-admin-password

P.S. The database file is stored under includes/configure.php under the root directory where zen-cart is installed.