Sewer drain blockage repairs:
The first process is to have the drain cleared by a high-pressure water jet unit. You may be able to hire one but it may be just as practical to have a drainage contractor come in and try to first of all remove the blockage.
Either way by following the directions given under Repairing storm water drain blocked by tree roots: Make sure you get the drainage contractor to mark out on top of the ground where he or she thinks the tree root blockage is located under the ground.