add class to h2 tag that wraps each month

Hello,

I have a list of events grouped by month. The names of the months are displayed inside an h2 tag.

How can I add a class to this tag?
Alternatively, where can I find this html?

The code I use: [events_list_grouped mode=monthly limit=9]#_EVENTDATES #_EVENTNOTES[/events_list_grouped]

I have searched a lot with no success.

Thank you very much

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