How to select power direction over USB-C
Method 1: Reverse/inverse the sides/plugs of the USB-C to USB-C cable. Might works or not.

Method 2.1: Use a USB-C to micro-USB(male) cable and a micro-USB(female) to USB-C(male) adapter.

Method 2.2: Use a USB-C to USB-A(female) adapter and a USB-A to USB-C cable.

Method 2 should always work. However you cannot use PD charge then.

Explain for method 1: I've heard C-C cables have sides to determine host / device. But I can't find the source. From my personal experiment, it depends on cables.