That's one of my disappointments with the new game. You can't make a soup or stew to restore health. I treat my half healthy elders by making sure I put them at the food bin a lot, and also putting them into the spa to relax. As in other VV games there is not a sacred area where they can spend time and reflect, which takes up a lot of time for them. The younger villagers can also have their health bar down, but it seems after a while they go back to normal health without doing anything. Good luck.