What should I do if the umbilical cord doesn't fall off?

Please expand. I agree please expand on your question.
Ok if <1 month. Although almost all cords fall off in the first two weeks of life, it is normal for the umbilical cord to take a full month to fall off. Most important is to keep the cord dry. There is a very rare disease in which the cord does not fall off by 4 weeks of age, so if it shows no signs of detaching at a month, or you see pus or skin redness around the stump, your doctor should check the baby.
Talk to MD. If it's been more than 3 weeks, talk to his pediatrician. Late detachment can indicate a problem.
Doctor can check it. If an umbilical stump hasn't fallen off by the 2-week check-up, it should fall off between the 2-week and 4-week check-ups. The doctor can check it in the rare case that the stump is still attached at 4 weeks. If there is an odor, or some redness around the umbilicus, a doctor should examine it for infection.
See your provider. Most umbilical cords separate by 2-3 weeks of age. Cords that do not fall off by 3 weeks of age may represent a serious immunodeficiency called lad (leukocyte adhesion deficiency). It's best to be seen by your medical provider if this is the case.
Unclear. Are you asking about what to do if the umbilical stump doesn't separate? If so, it should fall off by 30 days. Delayed separation of the cord can be helped with medication from your doctor if that is a problem.