I agree with Deborah's excellent advice!
I know from experience that weaning budgies onto pellets can take forever and be extremely frustrating. One of the best ways I've found is to do it in ratios:
Every time you change their food, add in a few more pellets, then a few more, then a few more (about a teaspoon more every two days) and after a week, the ratio should be at about 25-30% pellets to 70-75% seeds. At this point, they usually only eat the seeds, and then beg for more seeds, ignoring the pellets.
At this point, do not give in to their begging for more seeds. Many birds will only begin to eat pellets after there's no other option.
This seems kind of dramatic, but that was the only way my little girl learned to eat pellets, and now she loves them!
Eventually, increase the pellets until they are 50-50 with the seeds, and finally mostly pellets, then cut out seeds entirely. Budgies can go for 2 days without food, so don't worry if they don't eat. They're usually inclined to take a nibble during this time!
After a few days or so with just pellets, you can add seeds back in and offer like 1-2 tsp. of seeds separately.
Also, with ZuPreem fruitblend (which my little one eats), it's obvious when they eat them because their poop changes colours