Dissolve baking soda in water.

Pour the baking soda and water mixture into the spray bottle. Use a funnel if needed.

Spray generously along the grout lines.

Let the solution sit for several minutes to penetrate the mold.

Finally, use the scrubbing brush to scrub loose the mold. Scrub gently, as you don’t want to damage the surface you’re scrubbing on. 

Rinse clean with water. I usually wipe it clean with a dry cloth to prevent water stains.

Spray onto the grout a second time if needed and repeat the process.