purge interval filters

Dear all,
I would like to shorten the interval for DB purging, and I found that I should use this filter:
add_filter(“simple_history_db_purge_days_interval”, function($days) {
$days = 10;
return $days;
});

May I ask you where should I insert the filter? In simple-history/index.php or elsewhere? May you also please check if the syntax is correct?

Thank you,
regards
Pietro

https://www.ads-software.com/plugins/simple-history/