Marzipan is a pliable dough made of almond paste, sugar, and sometimes egg whites or meringue powder. It can be tough to work with and will harden if it's not stored properly. Similar to fondant, marzipan is used to make cake decorations or to cover an entire cake. It must be softened to make it workable. The degree of effort needed to soften marzipan depends on the degree of hardness or stiffness. Fresh marzipan, for example, requires very little effort compared to marzipan stored for six months in loose wrapping.
Knead the marzipan in your hands so the heat in your palms makes it more pliable. This is usually all that's needed when opening a fresh package of marzipan.
Place the marzipan in the microwave and heat it at full power for 5-second intervals. Knead it after each cycle until it's soft and workable. This helps to melt or dissolve the crystallized sugar in the marzipan, which is similar to microwaving crystallized honey to make it runny.
Add water or corn syrup to the marzipan a few drops at a time. Knead it in your hands before adding more.
Bring water to a simmer in a double boiler. Place the marzipan in the steamer basket and cover it with a lid. Check it after about 5 minutes in the steamer to see if it's rehydrated enough to work with. This measure might be necessary if you've left it stored for several months, particularly if it's not wrapped in plastic or stored in an air-tight container.