Repairing an underground sewer pipe involves several methods. Trenchless technologies like pipe lining or pipe bursting are minimally invasive, limiting excavation. Pipe lining involves inserting a resin-coated liner into the damaged pipe, while pipe bursting breaks the old pipe and pulls a new one into its place. Traditional methods include excavation, cutting out the damaged section, and replacing it. Professional assessment is crucial to determine the most suitable method based on the extent of damage. Always consult with licensed plumbers or specialists for underground sewer pipe repairs.