My procedure for replanting root bound plants, pictured is the Blue Ischia. I have been doing this for years on most garden vegetable plants that were root bound in starter containers.
The procedure is as follows:
1. Wash the roots in a "water bath" using agitation and water currents only (plant roots held underwater by stem, other hand creates water current by pushing water towards roots, like clapping).
2. untangle the larger roots carefully.
3. Root prune all the tips (if possible) to remove apical dominance and increase root branching.
4. Plant in prepared soil (garden or container) and fan out roots.
5. "Water in" to settle soil around roots.
6. Prune plant to balance for damaged roots and or for shape.
Due to the volume and size of the roots on the Ischia starts, I decided to up pot directly to 1 gallon containers.

<edit> for larger figs plants (1 gallon containers), I've used 5 gallon bucket for the wash basin.