Repacking Vivo Y12i firmware requires some technical expertise and the right tools. Here are the general steps:
Vivo Y12, Y15 Flashing Free Tool Dead Boot Repair Unlock Tool - YouTube. This content isn't available. YouTube·Mobile Easy Solution
If the device gets stuck on the Vivo logo, you likely have a checksum error in your repacked image. Ensure the file size matches the partition limits defined in the xml files.