I feed my adf
those same pellets, as well as frozen bloodworms. I turn of the filter, which is the signal food is coming, and I drop the pellets in the front corner of the tank, always. They are smart and will catch on quick to the feeding ritual you initiate. They see terribly, so they go mostly from smell, mine didnt quite "get" the pellet food idea until they were more trained to where to come for dinner. Now they come to the food corner and start snapping at whatever is there.
I feed my bloodworms a bit differently (same filter routine and corner) but I use a syringe with a little tank water and squirt the worms slowly down into thier corner, a few at a time. Once they eat those, I will give a few more. This helps to keep from overfeeding and making a mess of the tank. I also have a dwarf puffer in the tank who eats his bloodworms right from the tip of the syringe.
You can try feeding both the pellets and a couple bloodworms together in the same spot to entice him. Once he figures out those pellets are food, he will readily eat them.
Lastly, I see you use gravel, the pellets might be falling down into the gravel where he cant get them. Try getting a small saucer (like the bottom tray of a terracotta pot) and drop his food on the saucer. That way her can get to it, and will also become a routine for him.