Working in front of a computer full day is not good at all for the posture.
This is some execises I do on a very irregular basis (sadly), but which proved
to work.
Note that regular weightlifting with supervising coach is another good way to fix the posture...
Variants are W, Y, A, I, L, etc. each of them targetting different muscle group.
Lie face down on a mat or a comfortable but firm surface.
Extend your arms straight out to your sides, forming a "T" shape with your body.
Your palms should face down towards the floor.

image // workoutguru.fit
Do it gently!
Can be done with a bar, a stick or even a towel.
There's a variant where you start from behind the back and genlty pull the shoulder into extension.

Example from Men's Health
Raise both arms out to your side on an exhale.
Keep a soft bend in your elbows.
Squeeze the shoulder blades together as you pull them toward the spine.
Lower the weight back to the start position as you inhale.
Avoid hunching your shoulders, and keep your chin tucked to maintain a neutral
spine during the exercise.

image // men's health
The goal is to join your scapula together, exercising the rhomboid muscle.

image // training.fit
Can work with kettlebell or elastic band aswell.
Squeeze the shoulder blades together as you pull them toward the spine.

image // braingain.fit
Focus on the upper-back and shoulders.

image // workoutlabs.com