Wheelbuilding / Wheel Building / Wheel build help

A mate of mine has bought a CannondaleX SE with an offset hub position. Apparently he wheel need to re-dish any new wheels he gets by 6mm to cater for off set.

Does anyone know process for this and anyone that could do it?

Unless you're really lucky with spoke lengths, it'll need a fresh build with the correct lengths. Anyone who can build a wheel can build an offset wheel, especially if it's only 6mm, not 28mm like some fatbikes.