Scrape as much toothpaste off the garment as you can. Since it is already washed, you may only be able to get a little bit off, or none at all. The more you can get off, the easier it is to remove the entire stain.
Spray stain remover on the toothpaste spot. Let it set for 10 to 15 minutes. If the stain remains, spray on more stain remover. Let it set for another 10 to 15 minutes. Keep doing this until you notice a difference in the size of the stain.
Put the item in the washing machine, and wash it as usual. Check the stain when it is done washing. If it is gone, put it in the dryer to finish laundering it. If the stain is still there, spray more stain remover on, then wash it again. Do not dry the garment until the stain is gone, as you will further set the stain in the fabric.