Place the 6 oz sliced cooked turkey on a microwave-safe plate. Cover and microwave in 30-second intervals until the turkey reaches 165°F.
Squeeze excess moisture from the 1/2 cup sauerkraut with paper towels.
Stir together the 2 tbsp Greek yogurt, 1 tbsp ketchup, 1 tsp relish, and 1/2 tsp Dijon.
Spread the dressing over all 4 bread slices. Divide the hot turkey, sauerkraut, and 4 Swiss cheese slices between 2 slices of bread. Top with the remaining bread.
Spread the outside of the sandwiches with the 1 tbsp softened butter.
Cook in a skillet over medium-low heat for 3–4 minutes per side, pressing gently, until the bread is golden and the cheese melts.
