With the power off, locate the cut marks on the rope light at each end of the section to be replaced. Use a straight edge cutting tool like PVC pipe cutters or a single blade pruning shear to cut the rope light at the cut marks and remove the defective section.
Slide the heat shrink tubing over the rope light and install the splice pins and rejoin the repair section. Center the heat shrink over the splice and use a heat gun or hair dryer to shrink the tubing into place.
Be careful not to melt the rope light during this process but the heat shrink tubing does need to be very tight on the rope light.