A budgie who has always eaten seed will often have trouble recognizing other items as food. Here are some ways that you might be able to introduce your budgie to healthier foods.
Use their foraging instinct to your advantage.
If your birds are tame and can safely be allowed out of the cage, chop of veggies on a favorite spot such as a newspaper-covered table or a playgym. Allow the birds to "find" their food so that they feel they're foraging. This is how I converted some of my birds to pellets. Make sure the room is safe for your budgies before letting them out.
Use baby food!
Buy cans of baby food (vegetable types like carrots or green beans) and mix it with their seeds. This is a pretty good way to get some nutrition into them when they're still refusing to eat fresh foods. The ingredients in baby food are usually just a vegetable and water. My birds really like this.
Chop the fresh food up into tiny bits If you chop up the food into little bits, they may be more likely to pick at it. Put it into different food cups if you have a large cage and their foraging instinct might lead them to the new food dishes and cause them to nibble at what's inside. Add seed or sprinkle millet and mix it up. They will first eat the seed/millet but will get a taste of the other food and you will be surprised that with patience they will start to eat the new foods.
Hang leafy greens from the top of the cage near a favorite spot.
This is what most people try first. Just make sure to remove any uneaten portions after about two hours.
Make birdie bread Bird bread gives you the opportunity to put many different healthy foods into one "package." Here's one recipe that I found:
2 6 oz jars baby food sweet potatoes
2 jars baby food tropical fruit
1-1 1/2 cups pellets or 4 tbss hand feeding formula
3 eggs and eggshells (crushed)
I recycle pellets left in our birds' bowls (We use uncolored pellets). Mix eggs and baby food. Use a little in a small blender/processor to crush the egg shells (calcium source). Mix in remaining ingredients. Put in paper cupcakes or muffin tins- 4 tsps each. Microwave 1-2 mins until firm. Or bake in toaster oven at 400 degrees for 15 minutes till firm. Makes 12 servings. Serve warm, but not too hot.
Keep persisting and they will eventually start eating a healthier diet. Also, check into some of the other healthy foods that you can buy such as beak appetit or wheatgrass.
Try to offer the healthier veggies such as kale, carrot, spinach, broccoli as well as legumes such as chickpeas, lentils, and beans.
Check out this link about converting them to pellets it will also give you suggests about new food Pellet Diet
As with anything new be patience it may take months for your bird to finally try something new. NEVER CONVERT OVER COLD TURKEY Your budgie will starve itself. Don't have the mentality that the bird will finally get hungry and eat it doesn't work that way with birds. They see it as something that can harm them so they won't try. Always convert slowly.
Remember to never feed your birds the food listed in this link Unsafe Foods.