Sit back in the chair, pushing your bum to the back of the chair, and use the back of your seat as a support.
Next get your screen at the right height, it should be at eye level.
Try to have it directly in front of you and not off to the side.
I often get people coming in with neck pain on one side which is aggravated by continuously turning to the one side to either look at another screen or answer the phone.
The seat and desk you use are also important.
Try to have a supportive chair, not just the kitchen chair and desk wise dont have it too low that you are reaching down to your keyboard or too high that your shoulders are elevated.