baby cereal, better plain favour or plain congee, give one or two spoons at first, after that, still give milk, then increase solid gradually to replace one meal of milk
if for congee, can try adding vegetables like carrot, pumpkin one by one, try each ingredient for a few days to see if bb can adjust or any side effects, if progressing well, try minced meat, start from pork, then chicken, then beef/fish