How to correct bitterness in blended homemade salsa?
If the problem is just a little bitterness on the tongue, salt is usually the best foil. If you can find out where the bitterness came from by sampling other pieces of your raw ingredients, you can try upping the ratio of other ingredients to temper it. 

Advice more specific than that would require a crystal ball, I'm afraid. If it's really quite noticeable, then you're probably better off making a new batch with new ingredients.

Good luck!