Assuming you mean a gaming chair and not an actual chair:
There are a few things you can do to make your gaming chair more comfortable. One is to adjust the height of the chair so that your feet are flat on the ground and your knees are at a 90-degree angle. You may also want to adjust the backrest so that it's in line with your spine. Another thing you can do is add a lumbar support cushion or pillow to the back of the chair for extra support. Finally, make sure the seat is padded enough so that you don't feel like you're sitting on a hard surface for long periods of time.