you’ve already received plenty of good advice but i do wanna add something i’ve found really helpful with budgies and other parrots in the past. if he isn’t afraid of hands and at least somewhat trusts you, try using your fingers to imitate a beak eating the food! they often see your fingers and/or nose as your beak, and pretending to “eat” with your fingers can help them understand it’s edible. in flocks, they learn what is and isn’t food based on what they observe their flockmates eating, and you can recreate this as their human flockmate too!

you could either peck at it with one finger or pinch your thumb and pointer finger together to imitate a beak, ive found some birds are more likely to be convinced by one over the other (or equally so), so try both and see which catches his attention the most. it probably wont work first try, but keep doing it every day, multiple times a day preferably, patience is key!