You need to put a dye over it to eliminate brassiness. I would suggest L'Oreal Excellence or Preference hair colours in Light Ash Brown, if your hair is lighter than a brown right now than a Dark Ash blonde. A lot of people think using an ash will turn your hair green. This is only if your hair is much lighter than the colour you're putting over top or if your hair does not have any red or orange tone to it. (Example: Putting a Light Ash Brown over a light neutral blonde = green) I suggest leaving it on a couple minutes longer than suggested to ensure that your takes in the dye since you don't dye it often. After doing this it is a good idea to use a blue shampoo like Light Blue Shade to keep hair from going brassy in the future.
Try just putting one more over. You might have put something too light, try a light ash brown or dark ash blonde. I would try the Light Ash Brown just because you might need a bit darker to get rid of the auburn. Don't worry if it comes out a little dark. It will fade.
In the future just remember the colour wheel
blue is opposite to orange
green opposite to red
purple opposite to yellow
you need a cool shade to eliminate the warm shade.