View source for Modify GCode to restart 3D Print

* Load GCode in text editor
* Find lines like Z0.*:

 ;LAYER:0
 M107
 G0 F8400 X9.53 Y-66.192 Z0.4

The first line is the initial layer height and would start the full print.

Now search for the line with Z=*.* where *.* is closest to the already printed height

Note down the extruder relative position E*.* before that line. Should look like this one (if measured height is 30.4 mm):

G1 F1500 E440.37857
G0 F600 X44.668 Y-41.761 Z30.4

Replace all lines between the first Z0.* line up to before the one with the current print height with the extruder initialization command "G92 E*.*." Use the noted value:

 G92 E440.37857

Save and start print with that gcode...