[Plugin: Events Manager] How to filter times more precisely?

Hi, I want to produce three columns with the events_list_grouped shortcode.
1. Past events older than 1 month (from now on!)
2. every event between the past month and the next month (from now on)
3. Future events newer than 1 month (from now on)

In one of the tutorials (Create Your Own Event Scope) you use
$end_date = date('Y-m-d',strtotime("+1 day", current_time('timestamp')));

Can I alter this using “-1 month” for 1. and “+1 month” for 3.?
And how about Point 2?
Where do I paste the “add_filter”-snippet?
Or is there maybe an easier way?
Thanks for your advice.

https://www.ads-software.com/extend/plugins/events-manager/