Mix 2 parts baking soda with 1 part bleach to make a paste. Spread it on the grout to sit for 15 minutes. Scrub with a brush and let it sit some more. Rinse and repeat if necessary.

Here's one way to do it:

https://www.hunker.com/12000997/how-to-clean-shower-tile-grout#:~:text=How%20to%20Clean%20Shower%20Tile%20Grout%201%20Remove,cleaned%20and%20dried%20tiles.%20...%20More%20items...%20

The easiest way I know is get toilet gel cleaner. Depending on the brand it usually has a squirt top so you can squirt on grout only. Let sit overnight if you can, scrub gently in the morning and rinse.

A baking soda and hydrogen peroxide paste is what has always worked best for me. I would let it sit over night then scrub with a tooth brush.

Spray with CLR or bleach and let sit for a hour, then use a nail brush and give it a scrub.

Saturate the grout with lemon juice, a mild disinfectant that gets rid of grout stains naturally. You can also use white vinegar for chemical-free grout cleaning. Simply pour vinegar from the bottle into the cap and pour it over the dirty grout lines. Allow the lemon juice or vinegar to sit for 10 to 15 minutes.

https://www.hometalk.com/5102646/cleaning-tips-grout-tile

How to Clean Grout

This should help get it clean: https://www.youtube.com/watch?v=0zmuASQ7tNE

I use a tub and tile cleaner with bleach

Here’s a Hometalk link for you to consider. Hope this helps

https://www.hometalk.com/23803774/how-to-clean-grout-and-install-new-grout-that-won-t-stain

Additionally

Painted Tile Grout Refresh with grout pen

https://www.blesserhouse.com/painted-tile-grout-refresh/

How to Clean Grout and Install New Grout That Won't Stain

Hi Lucy: Here are a few sites that should help:

https://www.craftylittlegnome.com/the-best-homemade-grout-cleaner/

https://www.youtube.com/watch?v=nbOU5UZNsa0

https://www.hometalk.com/31413513/make-your-grout-look-like-new

https://homeguides.sfgate.com/touch-up-grout-20644.html

https://www.youtube.com/watch?v=ifeSybjr2RY

Make Your Grout Look Like New!

How long ago was the grouting applied? It could be that it is so old that it is no longer responding to your efforts at trying to clean it, or to keep it clean. In this case, it needs to be reapplied new and resealed again.

Hi Lucy, here are a few ideas, hope they help you, I would seal the grout once you got it clean,

https://www.stanleysteemer.com/blog/tips-tricks/how-to-clean-tile-and-grout

https://www.youtube.com/watch?v=qS30FQCk8sk

Zero shower tub and tile cleaner or Lysol toilet bowl cleaner in the black bottle. Wet and forget shower if you don’t have marble, it will clean everything and keep clean with no scrubbing. It may take a few applications to see results if seriously dirty.

Here is a post that might help - https://www.wikihow.life/Whiten-Grout#:~:text=Start%20with%20warm%20water%20and%20a%20nylon%20brush.&text=Simply%20spray%20some%20warm%20water,soap%20into%20the%20warm%20water.

Use a grout paint pen after you have cleaned it as well as you can

I'd use a bleach pen or grout paint pen

You can add some bleach carefully or a bleach stick https://amzn.to/2JZyzHp

Hello Lucy,

Use a Dremel to cut the grout out and re-grout or try Copydex or White Gloss paint and an Artist brush.

They are so many ways in cleaning tile and grout here are some of the best ways of how to clean grout in your shower & bathroom.