To get mold out of shower tile grout you can go to Walmart and buy some mold remover that you spray on the tile grout where the mold is and let it sit for 10 to 20 minutes and then use a scrub brush to clean the mold out of the tile ground.
You can also use an old toothbrush to scrub the mold out of the tile ground.
Or dampen the toothbrush and then dip it in some baking soda and scrub the tile grout mold with the baking soda and toothbrush.
The mold should start coming out of the tile grout and if not you should make a baking soda paste with some vinegar or water and then scrub the tile grout mold again.
If that doesn't work you might need to try some bleach which helps to kill the mold and helps to remove the mold as well with the scrub brush or tooth brush.
White vinegar also works at killing mold and removing mold naturally from your shower and shower tile grout but a toothbrush that you use only for cleaning purposes can work good for getting in between the tile grout to scrub the mold out of the tile grout.