Your bird is very sick and will die if not treated properly. Please take him only to an Avian Vet in your driving area because he may very well have a viral infection that can only be diagnosed through bloodwork and other tests not like bacterial infections.
You also cannot just change them from seeds to pellets because this make them sick if they eat at all. Here is a link on how to go about the change, and make NO CHANGES until this bird is back on its feet. Give it the diet it is used to having until it is well enough to change to pellets. Whoever told you to make a change like this so quickly does not know what they are talking about, so get it back on its regular diet.
Please get your bird to an Avian Vet as quickly as you can because he is going to die if not treated correctly by an Avian Vet. Regular dog and cat vets are not licensed or trained in care of birds and will give them the wrong meds and too much of it. Lots of times they kill birds trying to treat them like dogs and cats.
