What is best way to clean tan grout on floor??

Scrub brush and non bleach cleaner. Once clean, seal with tile/grout sealer

To clean dark colored grout lines on tile floors:

1. Mix baking soda and white vinegar in a cup to a paste like consistency.
2. Use a small brush to apply the mixture to the groutlines.
3. Allow the mixture to remain on the grout lines for a little while.
4. Use a small scrub brush or an old toothbrush to scrub the grout lines.

Bar keepers friend and a good grout scrub brush. If you can't getstains out, after it is clean, you can paint or stain it the same color or another color. After you get it clean and the way you want it, make sure to seal it to make it easier to keep clean.

Here are some tips: https://www.todayshomeowner.com/video/tips-on-cleaning-grout-lines-on-tile-floors/