The default reminder status for calendars in eM Client is set to "No Reminder", but you can adjust the default reminder in Menu > Settings > Calendar.
Scroll down to Defaults and click 'Set' for default reminder.
Here you can choose the time for your default reminder and if you want to assign it to all calendars or manually select which folders to assign the default to.

You can also change individual calendar’s Reminder in the Calendar section of eM Client.
Just right-click the calendar, select ‘Properties’ and change the Default reminder under the General tab. You can also change the color and other properties here.