Link — Ums5121h10natv Firmware Update
There is no universal "single link" for this firmware. The UMS512 is a System-on-Chip (SoC) used by many different manufacturers (Otida, B2C, Tenwe, etc.). Installing a firmware intended for a different board revision—even with the same chip—can permanently "brick" your device.
: Variations like H10 vs H20 or NATV (Native) vs specialized OS versions are not interchangeable. Flashing the wrong variant can permanently damage your hardware. ums5121h10natv firmware update link