Advanced re-batching has a few different steps than the basic method, but the smooth end result is well worth the extra work.
The items you will need for advanced re-batching/hand-milling will be everything you need to make a fresh batch of soap- oils, lye water (or lye milk etc) stick blender, other utensils you generally use etc.
and half of the soap you need to re-batch.
The soap you are re-batching should be shredded and ready to be re-batched.
Mix up half a batch of fresh oils, while melting down your hard oils, add in your soap shreds.
Now stick blend the oils and shreds.
Remember to use extreme caution as you are stick blending hot oil!! If your shreds are soft you can skip the hot oil and do it at room temperature.
I highly recommend softening your shreds with a bit of water and letting them sit for a day or two so you do not need to use the hot oil method.
Your oil will appear to thicken to a medium trace, don't be alarmed, this is normal.
Now begin to add in your cooled lye water and stir and stick blend until well mixed.
Trace is very hard to see because the oil/soap/lye water mixture is very thick to begin with.
You may have to go by time rather than sight for this procedure.
Stir and stick blend the same amount of time as you would if you were making an all new batch.
Add in whatever you will be using to color and scent the batch after a few minutes of stirring.
Your end result will be a thick trace looking soap, and will need the 3 week cure that is standard on fresh soap.