A few hours into 3D printing a dice tower for my son the print failed. As the print was going to take 13 hours in total, and the part that had been printed was good, we were reluctant to start again.
To print the rest of the model we used Cura to reslice the model starting at the point where it had failed. To do this open the file in Cura select the object and in the move options set the z-axis to the negative value of the height the print failed (we just measured the height of part that had printed). So if your print measures 47mm set the z to -47. This should sink the print below the bed.
We tested that we had the right height by printing a few layers of the new file, stopping the print, and testing how it fitted on the existing piece. Adjust the z position in Cura if necessary.
Once you have your print in two pieces you can use superglue to glue them together.