Heat skillet or griddle to 300 degrees. Grease skillet with 1 tablespoon butter. Spread 1 tablespoon butter on one side of each bread slice. Place one bread slice, buttered-side down, in skillet; top with both slices American cheese then spread the cream cheese evenly over the top. Place the second bread slice, buttered-side down, in skillet; top with both slices Swiss cheese then spread the pie filling evenly over the top. Cook until golden brown and cheeses are melted, 2 to 3 minutes. Flip the American cheese-topped bread slice onto the Swiss cheese-topped bread slice; cook 15 to 20 seconds longer. Remove from skillet; cut in half. Garnish with fresh blueberries.