PHP Compatibility Check says deprecated code in plugin

I am wanting to upgrade my PHP on my site to 7.3, and I ran a check through PHP Compatability Checker and an error came back for Hummingbird Pro:
FILE: /wp-content/plugins/wp-hummingbird/core/modules/class-advanced.php
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FOUND 1 ERROR AFFECTING 1 LINE
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530 | ERROR | Extension ‘mysql_’ is deprecated since PHP 5.5 and removed since PHP 7.0; Use mysqli instead
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How can I fix this so I can update my PHP and not run into issues?