From Ground: First, moisten the soil around the st. Bernard's lily plant with a gentle splash of water to make digging easier and reduce root damage. Using your garden spade or shovel, dig a generous circle around the plant, careful to get under the root ball without severing important roots. Once you've dug around the plant, gently lever it up with the spade, making sure all, or at least most, of the root ball remains attached.
From Pot: If the st. Bernard's lily is coming from a pot, water it well half an hour before your transplanting plan. Turn the pot on its side and, as you carefully slide out the st. Bernard's lily, grasp it as close to the base as possible, being cautious not to harm the root ball.
From Seedling Tray: Hold the st. Bernard's lily seedling gently by the leaves, not the stem, and pull very gently. If the seedling doesn't slide out with minimum resistance, use a spoon or similar tool to ease it out, ensuring most of the root structure and the soil around it comes out intact.