Any tips on baby coughing and having flu?

Hi my 7 month old baby has been having the flu for a couple of weeks and had even went to the KKH cos his oxygen level was down . Doctor mentioned that he just gotten a few flu viruses at once and it will take time to fully recover. So I was wondering, do any mom have any tips on helping to ease a baby’s nose congestion and cough? My baby seems to cough every night and he tends to swallow his phlegm back. Idk how/what I’m supposed to do. Does putting on air humidifier with essential oil works? What kind of essential oil to use? What other method there is? Really appreciate for this. #firstbaby #FTM #babyflu #remedies