You’ll need to draw shapes around the fingers, track them, and correct the shape where it moves off the finger edges. The magnetic spline tool can help with this, so can using alt/option S to snap shape edges. Since they’re probably not bending much, you can probably get away with rotoscoping one finger at a time. If they’re bending a lot, you’ll need to split the shapes up at the joints of the fingers. It will be tedious to roto. You might get better results doing a remove in that section that removes the fingers and the mic together and making a new track in Avid, putting a new instance of Mocha on that, and rotoing the fingers with motion blur on that layer. You can apply motion blur in edge properties.
You can track and roto fingers at the same time, but make sure you don’t use perspective when rotoscoping.
Try that and let me know if it fixes this for you.