Eclectus parrots are generally excellent eaters and will eat anything offered to them. The minority that are fussy eaters are usually those who’ve been raised on seed or pellet diets only and converting them to a healthier diet can be very difficult.
Eclectus that are on only pellets should not be offered additional vitamin supplements. Pellets already contain a large amount of added vitamin supplements in them and some pellet brands are known to contain extremely large amounts of vitamin D which can have devastating health effects on them.
If Eclectus is on a seed diet you can add vitamin supplements to their water or seed mixes until your bird is converted but you should consult your avian vet to get the correct dose of vitamin sups as well as the exact types of vitamins your bird is lacking. Presuming any of this can put your Eclectus in danger of an over dose of certain vitamins.
Alternatively you can can soak the seed in something like berry juice or carrot juice. It used to be common practice to 24 hour soak bird seed, thinking the nutrition levels were much better than dry seed however, recent studies have shown there is no difference in nutrition from dry seed to 24 hour soaked seed. Using a natural juice will be a good alternative to adding some of the nutrients from the juice to seed during the soaking.
Sometimes our ekkies become bored with the food they eat and this can stop them from eating. Keeping their meals & food interesting will prevent this. You can do this by offering skewers, foraging toys, hiding food throughout their cages & play gyms, making all kinds of recipes and shapes.
You can do things like hide pieces of food in honky nuts or any other edible nut shell.They can make a natural foraging toy.
You can also try adding a little peanut or almond butter to the foods they don’t particularly like to get them to try the new food. In most cases once they get the first taste of the new food they will be willing to eat it.