What do I use to clean and restore to bathtub grout? To remove mold

It is possible to clean the mold/mildew from the grout, but there is a chance it may stain permanently. Clean it with bleach water, rinse it well, scrub to get as much off as you can, a scrub brush or even a toothbrush may help. Once the grout is as clean as possible, spray the area with vinegar, no solution. Let that dry naturally, it will kill any spores remaining in the area. Hopefully this will help forestall the formation for a while. Try to keep the grout, tile, etc. dry between uses and it should happen less frequently.

Spray it with vinegar and then scrub with an old toothbrush.

This video might be able to help: https://www.youtube.com/watch?v=Nf-zAMUMC1Y

The bleach will de-colorize the mold, to apply it, you can use the cotton balls or paint it on with a brush. Rinse the next morning and then spray it with vinegar. The vinegar will kill the mold and spores.

Heat up 1 cup of white vinegar, mix in about 1/4 cup of Dawn Premium. Not the dollar store kind, because it is too thin. When mixed, pour into a spray bottle and fill with water. Shake. Spray down the grout and let it sit overnight. In the morning rinse. If you have stubborn stains, spray again. Use this mixture a few times a week. It will keep your grout and tiles clean. Also works wonders in the toilet bowl to keep hard water stains at bay. Oh you only have to heat the vinegar one time when you add the Dawn.

If you want to completely change the color of your grout. There is a product by Mapei called Grout Refresh. You can find it in Floor and Decor and Home Depot sells a few colors, but Amazon has many colors. It is not hard to use, just time consuming. I changed the color of my 2 bathrooms grout several years ago. It has a sealer that prevents stains, and it still looks brand new.

make a paste using 1/2 cup baking soda and several teaspoons of water. Using a brush, rub the paste on the mold-affected grout areas and let it sit for 10 minutes. Rinse the baking soda thoroughly and repeat to make sure the area is clean and mold-free.