You can duplicate your video layer and selectively mask in the finger with some blur on the mask. It’s not uncommon to have to clean up the roto like this, especially when there are blur issues.
In the future, it’s best to shoot at a higher shutter speed and remove the blur as much as possible. You can always add it in back later with the RSMB plug-in or pixel motion blur if needed (kind of sucks).
Best regards,
Kevin Camin