Select the image layer you want to blur paint on.
Choose Paint > Effect Brush > Blur Brush . To set the amount of blurring, choose Paint > Effect Brush > Blur Brush to open the Brush Options box, and adjust the Blur Strength from 0 (no blur) to 32 (maximum blur).
Drag the stylus on the area of the image layer you want to blur.
You can use any brush as a blur brush by setting Brush Mode to Blur in the Brush Options window.