If salmon filets have been frozen, make sure they are thawed completely.
In a small saucepan, whisk together the maple syrup, garlic, soy sauce, vinegar and red pepper flake. Heat over medium-low heat until the sauce comes to a low boil. Reduce heat to low and simmer, stirring often, for 5 minutes. Remove from heat.
Place thawed salmon filets on a plate or pan and pat dry with paper towels. Spoon the maple glaze over the top of each salmon filet.
Preheat air fryer at 390 for 3 minutes. Then, place the glazed salmon filets in the air fryer basket skin side down. Cook at 390 for 8 minutes. (No need to flip during cooking.)
To test for doneness, use a fork to flake the salmon. If the underside is no longer red, and a flakes easily, the salmon is done.
Serve right away while warm.