It is recommended that you unscrew the showerhead and submerge it in undiluted bleach for 30 minutes. Remove it from the bleach and rinse before screwing it back on the shower tap.
It is also recommended to replace the showerhead with one that produces fat streams, not a mist.
Many “low-flow” showerheads produce a fine mist that contains droplets with high numbers of NTM; small enough to enter the alveoli of your lungs. Replace such a “low flow” or misting showerhead with one that has large holes (greater than 1 mm diameter).
Joe Falkinham’s paper on Reducing Exposure to NTM, 202