Place the diced potatoes in a large pot and cover with cold water. Bring to a boil over high heat, then reduce heat to medium and simmer until potatoes are tender, about 12-15 minutes.
Drain the potatoes and return them to the pot. Add the butter and milk, then mash until smooth and creamy.
Stir in salt, black pepper, ground cumin, smoked paprika, chopped onion, and minced garlic until well combined. Set the mashed potato filling aside to cool slightly.
Lay one spring roll wrapper on a clean flat surface with one corner pointing towards you (diamond shape). Place about 2 tablespoons of mashed potato filling near the corner closest to you.
Fold the corner over the filling, then fold both side corners toward the center. Roll tightly towards the opposite corner, sealing the edge with a little water to secure the spring roll.
Repeat the rolling process with the remaining wrappers and filling.
Preheat the air fryer to 375°F (190°C) for 3 minutes.
Brush each spring roll lightly with vegetable oil on all sides.
Place the spring rolls in the air fryer basket in a single layer, leaving space between each. Cook for 12-15 minutes, turning halfway through, until golden brown and crispy.
Remove from the air fryer and let cool for 2 minutes before serving.