Orange Pi RK3399 User Manual page 22

Orange Pi User Manual Shenzhen Xunlong Software Co., Ltd.
4. Wait a moment then release the metal tweezers
5. Use a micro USB Type-C cable to connect device and host PC
6. Device should enter MASKROM mode
It would show the following with AndroidTools on Windows:
After this could flash the image in the normal way.
www.orangepi.org 19 www.xunlong.tv