How to feather one section of an alpha layer when there is no mask?

Hello, I hope this is an easy one...

I have an alpha+rgb video clip.  The video is of a man's face, with no background (transparant background)

I would like to feather one section of the man's face, but there is no mask and nothing to adjust.

I don't have the original files, just the video clip.

Is this possible?

Thank you,

Letty