Simmer cooking water and cooking salt in a saucepan large enough for whole potatoes. Add potatoes; simmer 7 to 9 minutes until outside softens, center firm. Drain; cool 15 minutes.
Coarsely box-grate potatoes into a bowl. Gently fold in flour, cornstarch, onion powder, seasoning salt, and pepper.
Divide into 24 equal heaped-tablespoon portions; firmly squeeze into cylinders about 1 1/4 inches long. Gently brush all surfaces with measured oil.
Preheat a 6-quart air fryer to 390°F for 3 minutes. Space 12 tots in one layer; cook undisturbed 7 minutes.
Carefully turn with tongs; cook 6 to 8 minutes more until golden and cooked through. Transfer to rack; repeat remaining tots.
Serve 6 hot tots per portion; refresh first batch in empty basket 1 minute if needed.