Asking this question indicates that this patient has a known association of the disease with UV exposure and the key at this point is to avoid exposure to UV rays by wearing long-sleeved clothing when going out and applying sunscreen and sunscreen lotion correctly.
If the rash is mild, it will heal on its own after sun protection; if the symptoms are more severe, with significant itching and discomfort, or even redness and running water, the patient should seek medical attention and be treated accordingly under medical supervision.