In order to update your database password within the wp-config.php file, you will need to login to your site via SFTP and navigate to the /web/content folder and look for the wp-config.php file.
You will then want to right click and view/edit the file. This will open the wp-config.php file into a text editor where you can then look for the section titled MySQL Database Password.
You will want to delete the password currently showing which is located in between the ' '. Once deleted you will add the password you set between the ' ' and then save the file and re-upload it to your site. Now you've reset and updated your database password!