Summarize this article:

Pour it slowly over your tongue, making sure to get the warm water in the area of contact between the metal and your tongue. This should raise the temperature of the metal, allowing your saliva to unfreeze.  You also want to make sure that the water is not too hot. No need to add a burn on your tongue to your list of problems! Don't pour the water too fast. Pour it slowly and steadily, so that the warmth works its way into the frozen connection. If your tongue is only lightly frozen to the metal, you can gently pull it off. However, if this process begins to hurt your tongue, stop and find a different solution. Try to twist your tongue and pull it off; hopefully this will cause your tongue to become unstuck. Let the hot air move out repeatedly until your tongue becomes unstuck. You may need to cuff your hands around your mouth, so that the hot air stays around your tongue. Do this multiple times until the metal warms up enough to unfreeze your tongue.

Summary:
Use warm water on the tongue and metal. Use your free hands to gently free your tongue. Breathe in deeply and then blow out hot air over your tongue.