Girls, hello. Could you please tell us if it's already a week, it's co…

Girls, hello. Could you please tell us if it's already a week, it's cold at home, the child started coughing and whistling with his nose. What should we do so that the cold doesn't get worse and how to clean the nose? I forgot everything already?. The pediatrician was only yesterday and everything was normal, today it started in the evening.