By default, frm_logs_cron_remains is set to '-1 week'. Use this code example to leave log entries that are one month old or newer. It can be adjusted to '-1 year', '-1 day', etc.

add_filter('frm_logs_cron_remains', 'logs_cron_remains_extend');
function logs_cron_remains_extend() {
    return '-1 month';
}