Side key of power button and fingerprint sensor is not working

@shantnuheer there are a few things you can try first. Make sure that you have the latest software updates download. You do that by Settings > About Phone > Software Updates > Download and Install > and check theere. If nothing is to be downloaded you have the latest software.

Now, since you power button does not work, you cant do a reset.it does look like you can run the Running the Diagnostic Tools under the Samsung Members app.

Run Samsung Members and select Get help on the lower half of the screen.

Tap View Tests located under Diagnostics.

Diagnostics checks, Individually Tap the following.

     Touch Screen; Buttons

Follow the on-screen instructions to complete the check.

There si more about what you can check on the Samsung Site

If none of that works, you will have to disassemble your phone and most likely replace the Fingerprint Sensor flex cable. since iFixit doesn't yet have a guide for that, use something like this video to work on it.

While you work on that, take lots of pictures. Once you are done with it, take those pictures and create a guide for iFixit. That will help the next person that has the same problem as you do. It's easy and fun to create these guides. https://ifixit.com/Guide/new The iFixit community will appreciate this.