We use saline spray and the snot sucker! I've heard good things about some plugins too but not tried them!
Calpol saline spray, Vicks humidifier over night Sitting in the bathroom with shower on hot
We brought our LO into the bathroom after the shower every day (about 5 mins) for about a week and that really helped. The steam was great 😊
Tummy time seems to bring out the snot as well, then use the saline spray and snot sucker. There is a vapour bath bubbles you can use from 3 months, I used to use it in the shower while she was on the bath mat and also when she has a bath
I use saline spray to try to make my boy sneeze.