You can toast in a slow oven or in a dry pan.
I often toast in a preheated dry pan over med-high heat. Pressing the chilies to the pan bottom with a flat spatula will help them toast evenly but do this briefly then flip them, repeat, stir or toss, then remove to a plate to cool. You're looking for some nice toasting--some nice toasted aromas--but take care not to burn. The process should only take 45 secs-1.5 min or so, depending on the chilies. Further drying will occur as they cool and then they can be ground.