Last six month data on Trend line using month & year parameter

Hi Tableau Gurus ,

I need to show last six months data on trend line

• It should have year parameter .
• It should have month parameter.
• If i select January from parameter control then data has to show from January to August like that  on X- Axis and trend line should change according to month's selection.
• I know it can be done using datediff but please give me clue using sample TWBX .

     I am wanting for your valuable help .

Regards ,

Bhuwan Vikram Singh