How can you study or prepare for an exam when you know that you have not done well on your previous tests, and you feel this time will be the same, not to mention others around you tell you the same

Hi, don't study and don't prepare to get pass or to do well in exams, study and prepare your to get fail in your exams..
Just study your subjects not for your exams, study for yourself to learn what is
In that subject that you don't know.
Wishes to fail in your exams.Best for your exams.

First I would practice some mindfulness to get your mind into wise mind instead of emotional mind. If your mind drifts to other things while doing this acknowledge and then bring your mind back to the exercise you have chosen. Do no judge just acknowledge it.
Once you are in wise mind you can begin studying. Again just acknowledge when your mind wanders and bring it back to the task at hand. Make sure to give yourself short breaks when you need them, make sure you eat healthy and get plenty of rest as all of that can contribute to not being able to concentrate.
Some examples of mindfulness are:
Color a picture and focus on just doing that. Don't judge how well you do, if you go outside of the lines, what colors you use etc. Just color
Look at a picture and just focus on it and what you see. Don't judge the picture just focus on it
Listen to music and hear the different instruments, hear the voices, listen for the music to go louder, softer, etc. Enjoy the music
Breathe in saying just this breathe in.. Breathe out saying just this breathe out. Focus on your breathing only
Those are just some examples. I am sure you can come up with more for yourself.