First of all, reduce processed food because hidden sodium causes bad water retention. Drink plenty of water—yes, drinking more water actually flushes out the retained fluids. Keep moving your ankles in circles when sitting at your desk.
Water retention is so annoying, yaar! My feet looked like bloated balloons in my third trimester, actually. The best thing is to keep drinking lots of water and sit with your legs elevated on a pillow whenever you can.
Pehle toh namak (salt) thoda kam karo, extra pickles and papad avoid karo. Keep your feet up on a stool while sitting and don't sit cross-legged. If the swelling increases suddenly or is on your face, call your gynac immediately.
Swelling in hands and feet is so tiring during these months. Just try to take enough rest and don't stress yourself with too much standing work. Coconut water also helped me feel better, hope you get some relief soon.
Daily gentle walking for 20-30 minutes really helps improve circulation and reduces swelling, but only do it if your doctor has allowed physical activity. Also, make sure you don't stand for too long. If your gynac permits, some light prenatal yoga stretches can also give great relief.