With the wear and oxidation of the protective case (sleeve) caused by the normal use of the mobile phone, the case (sleeve) of the mobile phone may appear slightly yellow, which can be wiped with a rag dipped in a small amount of alcohol. If the mobile phone case (cover) has turned yellow, it is recommended to replace it with a new one. For the models under warranty, you can go to the service center to replace the protective shell for free. You can check the address and telephone number of the service center on /vivo's official website/My after-sales website. It is suggested that you bring a valid purchase voucher and warranty card, and make a phone call before you go to ensure that the protective cover is in stock and collected by the staff, so as not to waste precious time and make a trip in vain.