It may seem like bleach would be the answer here, but it's not. It will lighten the mold, but it may not kill it. You want to stop it in its tracks. Here's my go-to recipe for cleaning moldy surfaces.
Fill your spray bottle about ¾ of the way with the vinegar. Top with warm water. Add 30 drops of essential oil for a 16-ounce spray bottle. (Use more or less for smaller or larger spray bottles.)
Shake well and spray on the moldy surfaces. Allow it to sit for about 20 minutes before rinsing it off.
For mild cases and routine maintenance, this should be enough to keep it clean. For severe cases, you may need to wipe or scrub with a soft brush. Once your shower is clean, add another thorough spritz to keep it clean.
This mix will keep for a few weeks if you use distilled water and shake it every time you use it.
Recipe by DIY Natural at https://www.diynatural.com/mold-in-shower-mildew-homemade-cleaner/