Fix Wordpress error

A site that was built a few years ago with an older theme that is no longer supported is showing an "error establishing database connection". Need to reconnect to the database, possibly restore/repair the database to show the old site ideally, or at least save some of the content, even if the theme is beyond repair. If all else fails, then installing a fresh WP instance. Here's what debug is showing:

Warning: mysqli_real_connect(): (28000/1045): Access denied for user 'username_here'@'localhost' (using password: YES) in /home/naturalw/public_html/wp-includes/wp-db.php on line 1529

Deprecated: mysql_connect(): The mysql extension is deprecated and will be removed in the future: use mysqli or PDO instead in /home/naturalw/public_html/wp-includes/wp-db.php on line 1559

Warning: mysql_connect(): Access denied for user 'username_here'@'localhost' (using password: YES) in /home/naturalw/public_html/wp-includes/wp-db.php on line 1559
Error establishing a database connection

This needs to be done asap. Estimating 1-2 hours for this, but will want to know if more time is needed.

Thanks!