Welcome to EmpowHER. Are you asking if you need to eat a non-vegetarian or non-vegan diet? Or, are you asking if you must eat a vegetarian or vegan diet? Has the physician who made the diagnosis suggested that diet will help this rash?
The exact cause of pityriasis rosea is unclear. Some evidence indicates the rash may be triggered by a viral infection, particularly by certain strains of the herpes virus. But it's not related to the herpes virus that causes cold sores.
I am not aware of any diet that will affect the course of this rash.
Here is the link to this website's Pityriasis Rosea home page.
You might find information and community conversations helpful.