A common mistake is using MediaTek (MTK) tools on the Unisoc chip. Here is the correct tool breakdown:
: Flashing will wipe all user data (photos, apps, contacts). Back up everything first.
Open the SPD Upgrade Tool or SPD Research Tool on your PC.
Flashing means writing a fresh copy of the device’s firmware (operating system) directly to its internal memory. For the Nokia G21, this usually involves installing the (depending on region and update).