If they are afraid of your hand, try offering a very long spray of millet so they don't need to get that close. Hold it still and read their body language to see if they are interested. Don't chase them with the millet. Let them come to you. It might take some time. Try again later, if you don't succeed the first time. Be patient.
If that is still too much, go ahead and drop the millet in the cage, remove your hand, and stand nearby talking in a happy voice. Spend time next to the cage doing other things. Offer millet through the bars without reaching inside. The goal is to make your hands and your presence near the cage have lots of good associations and very few bad associations. See if you can find any other favorite treats - sunflower seeds, nuts, bird bread, nutriberries, whatever. Be the happy treat-bringer for your birds. Encourage them and build up their confidence around you.
Any time they seem scared, back up a step or two and give them more distance until they feel safe again. Sometimes you end up doing some back and forth ... they accept millet from your hand today, but tomorrow it is too scary. That's okay. Expect some set-backs. Move at the pace that is most comfortable for your birds.