[Hummingbird] php compatibility

Hello I have a problem with the plugin Hummingbird pro this is the eroor :
FILE: /home/arkaybev/public_html/wp-content/plugins/wp-hummingbird/core/modules/class-module-advanced.php
------------------------------------------------------------------------------------------------------------
FOUND 1 ERROR AFFECTING 1 LINE
------------------------------------------------------------------------------------------------------------
512 | ERROR | Extension 'mysql_' is deprecated since PHP 5.5 and removed since PHP 7.0; Use mysqli instead
------------------------------------------------------------------------------------------------------------
What can I do?
Thank