Change in Fiscal Date pattern for the exisiting company

We are required to change the Fiscal Year pattern starting from Oct 2019.
Current FY Date Pattern is April to March.  Company currently in FY 19 and Transactions for April 19 to Aug 19 is recorded in F0902 with FY 19.

Starting from Oct 19, we need to follow FY 20.  We are targeting to post new transaction starting from Oct 19 to FY 20.

When we tried to create New Date Pattern as Oct to Sept and apply the same in Company Constant, system is still capturing the FY 19.
The FY 19 is capturing is from Date Pattern Table F0008. When we created new Date Pattern as 1st Oct 19 to 30th Sept 20, system captured FY 19 as default from Period 1.