as Will linked to, GcodeSplit - Split gcode files by toolpath is a browser-based tool to help you split gcode files. Having said that, I would very highly recommend a bitsetter, it makes it much more accurate (the machine automatically measures everything) and painless (it’s just one go).
the bitsetter is by far my favorite add-on to my shapeoko 3XL … before I dreaded designs with multiple bits and now… much more design freedom basically.