“Dry rot” is actually a form of wet rot – it just feels dry. All wood rot in Australia is wet rot of one type or another.
A good first step is to flush the effected area with methylated spirits on a hot day. The evaporation process helps draw moisture to the surface where it can dry off. If the timber is not too far gone spray or brush on Earl’s Wood Hardener. Earl’s solidifies rot-effected timber into solid material. For deep rot you may need to drill holes in the rotten timber so the fluid permeates through. You can then fill over the timber with builders bog or exterior filler as indicated. For severe rot you may need to replace the effected timber.