Hello there. Although I don't like to assume things, I'm going to assume you have some Cognos experience.
To schedule a report for last month's data, you need to build out your report and be sure that Sent for Payment Date is one of the data items on your report. Then be sure to go into the Common Report Header Filters folder. Look for a folder labeled Filters Based on Sent for Payment Date. Expand that folder, then select the Last Month filter. This will ensure the report you run only pulls data from the previous month.
Once you have created the report and saved it in your My Folders, go to your My Folders and look for the icon below:
This will take you to the scheduling screen. On the scheduling screen, be sure the setting look like the following:
This should be what you are looking for.