3 month old with a cold

What can I do to help my 3 month old who has a cold??

I took her to the doctor on Tuesday and he didn’t seem too concerned, and just said it will clear up on its own.

She’s not really sneezing or coughing a lot but she has a lot of mucus built up in her chest/throat and you can get every time she breathes.

What can I do to help??