Our little girl is 7months and gets congested quite often.We have been using snuggle babe vapour bubbles in her bath then the rub afterwards plus olbas oil on a tissue under her cot sheet for through the night. We also tried the Calpol plug in but it can be quite strong depending on the size of the room x
Steam helps. Take or run a really hot shower so the bathroom gets super steamy then (making sure the baby doesn't get too hot) sit in the bathroom with baby for a little bit. Depending on her age vapor rub helps too. They have ones for 2 months or older.