There is no easy way to do it.
It takes me at least 30 minutes to split a model as large as a chest piece into small enough objects to print onto my print bed.
Same time frame as a helmet. Things that require less than 8 pieces, however, are much easier and maybe about 15 minutes or less.
If you are going to get into 3D printing, this is one of those skills you are going to need to hone. Give it another shot and let me know if you still need help.