For MediaTek-based models like the Y12s (Helio P35), the SP Flash Tool is commonly used.
To manually flash the stock ROM, you typically need the following: vivo-y12s-pd2036f-stock-flash-file-firmware-rom
You can clear user data by holding Power + Volume Up to enter Recovery Mode and selecting "Clear Data". Warning: This will erase all photos, contacts, and personal files. For MediaTek-based models like the Y12s (Helio P35),