I'm sorry to hear that this has happened. I recommend that he speak with a doctor
. Recovery from a meniscus injury
can take a very long time. This is because the meniscus cartilage has very limited blood flow, and so it heals very slowly. Many people without very demanding physical jobs or participation in competitive or vigorous athletics may not completely recover to the desired level without orthopedic surgical involvement. However, many others with less demands on their knees may do very well indeed with medications to control pain and inflammation. Additionally most people with this injury should participate in a regular physical therapy program, as this can also help to strengthen and stabilize the need and help return to normal functioning.
Other than pain medications and physical therapy (and potentially knee bracing) there is not much else that can be done without visiting an orthopedic doctor. This is because cases that do not respond to these basic measures often do end up needing knee surgery, and this is the special area of an orthopedic surgeon
It is not clear from your question whether or not he is participating in physical therapy. If not this would definitely be very helpful, and it would be a good thing to talk with his doctor about.