Download Vivo Y28 flash file and official OTA update from the link below and follow the instructions after download link to learn how to flash. The first Vivo Y28 flash file here requires PC to flash. while the second firmware is an SDcard update package- in which case, it can only be flashed from your phone’s storage (sdcard).
If you don’t know how to flash or install the firmware from your sdcard, after downloading the firmware from the link below scroll down to find flashing instructions.