我該如何處理這case .?

Too risky. A business is a business. You are liable for any consequences as you have signed the form with your full private details and the form is undated. Unless you have studied and fully aware the implications of the terms in the form as far as your position is concerned, there maybe some terms that are unfavourable to you. You maybe obliged to do something to meet the requirements as an agent or else a penalty be charged on you. Go and ask your friend to return the form to you for detailed study and think of your position in this aspect then. You may, of course, get some assistance or further clarifications by calling Usana in respect of this membership thereof.