Canon GX7 mark 3 long exposure setting

the advanced mode dial is turned to m (i.e. full manual mode);

use the wheel behind the shutter to adjust the shutter speed. The minimum speed can be adjusted to 3 seconds, or it can be adjusted to Bulb (that is, door B);

fix the camera on the tripod and shoot with cable release (door b).

there are two ways to expose for a long time. one way is to turn the mode dial, that is, the thing marked TV, AV and m on the upper left, to TV, so that you can set the exposure time yourself, and the aperture will be matched by the camera's automatic metering.