First an foremost, call your vet, I am shocked he didn't show you how to do it.
Heres what I would do, although I must say this is very dangerous and you need to do this with caution.
You need to get your bird into a safe hold. Put your index finger and thumb fimly; but not too hard, around the bird's neck under the jaw bone. Then your other three fingers are used for back support. This is so she can't bite you, hurt herself, and you have a better chance of getting her to eat the food.
You can also wrap a washcloth around the bird, you may find this easier, because when I first learned how to hold a bird properly I found that holding them in a towel was easier.
Next-
When you have the bird in your grip you need to poor a mouthful of food into the bird's mouth. Chances are she will swallow some of it.
NOW there are other ways, but I have found that the way I told you is the most safe, and since your new at this I figured that would be the way to go.
Call your vet if this way does not work, becuase he is the only one who can show you how to forefeed down the throat, that is why I am so shocked he did not show you how to do it.
post if you have any other questions, or if I wasn't specific enough for you.