To relax your neck, tilt your head forward, backward, right, left.
Twist your wrists, make a few rotational movements with your shoulders back and forth. Tighten your abdominal muscles for a few seconds, then relax; repeat several times.
To stretch your ribcage, straighten your back, take a deep breath and spread your arms wide, as if you want to hug someone.
Stretch your legs under the table, feel the muscles stretch, rotate your toes, do the scissors exercise 8-10 times. If possible, walk around the office, first on your toes, then on your heels. This normalizes blood circulation in the legs, which is impaired if a person sits all day.
Take every opportunity to move. Walk up the stairs; if possible, resolve issues with colleagues personally, and not by phone or mail, etc.