Appears this problem, please complete the following steps to solve it:

1. Download corresponding model's ANDROID firmware package and brush the ANDROID firmware again.

V919 3G Air dual OS(V1,V2,V3 vesion): 

V919 Air dual OS(V1,V2,V3 vesion): 

2. Download windows8.1 firmware package(this is for V919 3G Air and V919 Air dual OS V1/V2/V3 vesion:

3. After install Android and win8 systems, boot and enter the windows8.1 system, connect to the Internet and activate windows8.1.

4. Download and install windows10 update tools: 

5. Operate windows10 update tool, the tablet will be connect to the Internet to download window10 system and start upgrade.

Note: This is only for V919 3G Air dual os and V919 Air dual os V1/V2/V3 version, V5 and V7 version V919 3G Air dual os do not exist the problem and can download windows10 update tools to update directly.

Onda V972 Android Tablet V1.35 Firmware Download