Using the taping knife, apply joint compound to drywall, slightly beyond where the edge of the corner will be.
Or use hopper to fill bead. Place corner trim on wall, ensuring it is aligned tightly to the ceiling. Press into position. Use the roller to embed the trim. Or embed using even pressure, running the knife over it at a 45° angle. Use the taping knife to skim over the edge with joint compound. Let dry thoroughly. Use the wider finishing knife to skim over the edge again. Let dry thoroughly. Lightly sand and paint.
For more detailed application instructions, refer to the Optimus Data Sheet.