If you switch between cold air and hot air when you blow dry your hair, it makes your hair nice and shiny.
If you use both hot air and cold air when you dry your hair, it gives your hair a nice shine.
ーIf you switch between cold air and hot air when you blow dry your hair, it makes your hair nice and shiny.
「ブローする時に、冷風と温風を交互に使ったら髪がツヤツヤになるよ。」
switch between cold air and hot air でドライヤーの冷風と温風を交互に切り替えることを言えます。
blow dry で「ブローする・ヘアドライヤーで乾かす」
make one's hair nice and shiny で「髪をツヤツヤにする」
ーIf you use both hot air and cold air when you dry your hair, it gives your hair a nice shine.
「髪を乾かす時に、温風と冷風を両方使うと、髪にツヤが出るよ。」
use both hot air and cold air で「温風と冷風両方を使う」
gives one's hair a nice shine で「髪に良いツヤを与える」=「髪にツヤが出る」
ご参考まで!