Hi Christine, I know that to be the advice given to anyone planting a fig tree and assume that this would be one of those exceptions to the no dig situation …! I have mine in a large dustbin and have yet to have any figs off it (nearly but not quite). I would certainly prefer to put it in the ground as watering is a pain.
I presume you would have to make the hole bigger than you currently need for the size of plant but you wouldn’t want to be digging it all up again…..
I’d be interested in what you decide to do and how it goes…