How to change/add/remove alerts for multiple events simultaneously
As from title. I need to modify the alerts of multiple events simultaneously. I know there is a feature to setting a default alert time when creating a new event, but this isn't that I'm looking for.
For example, I have 12 events this week and 9 of them have a alert time set to 1 hour before and I would to change it to 30 mins before without having to change each event one by one.
I'm using OS X El Capitan 10.11.3.
MacBook Pro, OS X El Capitan (10.11.3), mid 2011