Bring cooking water and cooking salt to a simmer in a saucepan large enough to hold the whole potatoes. Add potatoes and simmer for 7 to 9 minutes until the outside softens but the center remains firm; drain and cool for 15 minutes.
Grate potatoes on the coarse holes of a box grater into a bowl. Fold gently with flour, cornstarch, onion powder, seasoning salt and pepper.
Divide into 24 equal portions, about a heaped tablespoon each, and squeeze firmly into short cylinders about 1 1/4 inches long. Brush all surfaces gently with the measured oil.
Preheat a 6-quart air fryer to 390°F for 3 minutes. Arrange 12 tots in a single layer with small gaps and cook for 7 minutes without moving them.
Turn each tot carefully with tongs and cook for 6 to 8 minutes more until golden and cooked through. Transfer to a rack and repeat with remaining tots.
Serve 6 tots per portion while hot, refreshing the first batch for 1 minute in the empty basket if needed.