Root pruning is the only pruning needed for containerised fruit trees.
Before placing your tree in a new container, gently lay the tree on its side, and inspect the roots. Using a sharp serrated knife, remove about 25% of the root mass by slicing off thin strips from all around the root mass. Pry the root system free so that it spreads outward. At this time, if needed, prune 25% of the top branches.