Dates selected within reports are relative to when you set them. In other words, if you filter a report to the month "September 2019", the report will automatically adjust to showing the month of "November 2019" once the current date moves to the next month.
Here are the steps you want to follow to get a report to always send data for the last month or last X days:
- Setup the report and filter to the time period you want relative to today. ie. if its current November and you want last months data, filter to October.
- Save the report
- Optional: Setup a subscription to have the report emailed automatically.
For more information, navigate to steps two and three under "Subscribing to Customized Reports" here: Actions and Subscriptions