How to Aggregate Date and Apply it to an existing Flow

[Grant_Long]

Hi Power Automate Community,

I am having some issues with an existing flow. The flow is made to take a business contact (owner_name) and sort them by their account (account_type) and then add the amount earned (Opp_amount) per contact

There are many contacts and 5 account types, each with different quantities

So far I only have it adding up the total throughout the entire SharePoint list, but now I have to sort it by date (close_date), more specifically, on a monthly basis. 

the flow is a basic analysis

Get items -> Select -> Initialize variables -> Set variables -> Calculate

How would I add a way to aggregate all information by month? 

Thanks for any help that can be offered!