Filling blank cells from same column values

Thanks for the reply from AntrikshSharma , please allow me to provide another insight: 
Hi  Anonymous ,

Here are the steps you can follow：

1. Create calculated column.

New_Launch_Date =
MINX(
    FILTER(ALL('Table'),
    'Table'[Product_Category]=EARLIER('Table'[Product_Category])),[Launch_Date])

2. Result:

Best Regards,

Liu Yang

If this post helps, then please consider Accept it as the solution to help the other members find it more quickly

I created a New Launch Date Column =
IF(ISBLANK('Table'[Launch_Date]),
CALCULATE(MIN('Table'[Launch_Date]),
FILTER(ALLNOBLANKROW('Table'), 'Table'[Product_Category] = EARLIER('Table'[Product_Category] )), 'Table'[Launch_Date]))

This worked for me !! Thanks everyone for your time !!