I'm sure someone has a workaround for this but it'll be easier to answer with a packaged workbook with sample data. If you're dealing with sensitive information, I would check out Anonymize your Tableau Package Data for Sharing.
1 of 1 people found this helpful
If you are looking for a customized forecasting model then in Tableau Desktop & Tableau Server you can achieve this using the R-scripts. For more read here: https://boraberan.wordpress.com/2014/01/19/using-r-forecasting-packages-from-tableau/
If you just want to implement Last 3 Months that's possible using Filters. Pls share your workbook to be more specific.