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There is no one-click automated solution for that kind of work in any application that I know of. It all requires some manipulation by a user that has some skills. If you stabilize the motion of the hand so that it does not move in the frame creating the matte (masking or rotoscope) will require less work, and replacing the background will also be more accessible. You could time-shift a copy of the original footage to fill in the holes you leave when the fingers are removed. You may also have to create or paint two fingers to overlay on the hand to make it look like he still has fingers. When the composite is finished, it is easy to remove the stabilization in the main shot and add the motion to all of the layers required to complete the effect. The amount of time needed to produce this type of effect shot depends entirely on the shot. It can take between a few minutes a frame to a few hours. It all depends on the original footage. 

The same thing applies to changing a shirt to a sweater. The project could take many hours per frame, or if the footage is shot correctly, a 3rd party effect called Lockdown could shorten the workflow to a few minutes. You can work some amazing magic in After Effects, but it takes practice and experience to make the job easy.

The technique your're looking for is "rotoscoping." It's essentially the same idea as doing it in Photoshop but instead of just one frame it's doing it across multiple frames. You could go frame by frame and do it one at a time, but software can help with the process by analayzing the frames for you. But you don't want to do this in Premiere.

After Effects is the tool for this job. If you have the full Adobe subscription then you can install that program. Then look up tutorials on a tool called the ROTO BRUSH. You're going to be using it to track around the fingers you want to remove; when it's done it will have created a moving mask and the removed fingers will be black (alpha channel). You'll have to replace the background behind the missing fingers too.

If you need further help with it, I suggest posting in the After Effects forum. 

HTH,
JVK