How To Clean White Grout From Floor?

Yes, Winter2007 is right, and I know there is one that is like a pen or pencil so you can get in the little grout lines.  Not sure how well that works though but I'll bet it's pretty good.  They advertise on TV so you could go to the web site: As Seen On TV and look up the product by description and then check out the consumer reviews.  I find that very helpful for various products.

Yes, there is a product called bleach pen by Clorox.

As weird as it sounds, you might also try toilet cleaner that has
bleach in it.  The nozzle allows you to apply the cleaner directly
to the grout.  Be sure to check labels in case any product you
plan to use might be harmful to the grout.  Good luck!