Why is he using Head & Shoulders, does he have dandruff? If he is thinning he should be avoiding sulphate surfactants.
There is nothing one step that will control frizz AFAIK
, especially not if its damaged. Best thing you could do would be to get a rich cleansing conditioner than can also be used as a leave in, then have him wash with that, apply some to dripping hair and air dry.
2a-2c, medium texture, porous/ colour treated. Three years CG, growing out mechanical and chemical damage = breakage and very high porosity. Past armpit length heading for waist.
CO-wash: Inecto coconut
Treatments: Komaza Matani, coconut oil, Hairveda Sitrinillah
Leave in: Fructis Sleek & Shine (old), Gliss ultimate volume, Inecto argan
Styler: Umberto Giannini jelly, Boots Essentials gel
Experimenting with: going back to basics