First, a diagnosis of pre-cancerous rash is important. Precancerous pertains to something that is not yet cancerous, but appears to be on its way to becoming a cancer. You have to clarify what kind and where the rash is located as treatment is individualized. The usual procedure is to remove the rash through surgical excision or laser or cryotherapy treatment. There are other options such as topical medications. It is best that you have the rash evaluated and proper diagnosis is made to know which treatment option is best suited.