Apply a cold compress to the area every two hours.
Literal
2-hours every [at-に] affected-area [object-を] compress-[command-しなさい].
局部 'the affected area, the local area' — in medical context, the specific body part being treated. 湿布する 'to apply a compress.' しなさい is a mild command — typical of a doctor's instruction. ２時間毎 'every two hours.'