When you have mucus in your lungs usually some warm liquids such as warm tea will help to loosen up the mucus caught in your lungs which makes it easier to cough the mucus up.
Taking a steamy shower can also warm your lungs up and help to clear the mucus or using a humidifier to add humidity to the room you're in.
Other things you can do is to elevate your head and add some honey with the warm tea and then try coughing up the mucus using your stomach muscles which is known as a deep cough or even Huffing which seems to help me clear mucus out of my lungs when it doesn't want to come out.