Hello Kirill,
If you need to change the default accuracy for cameras/markers you should assign a three-component vector to chunk.camera_location_accuracy or chunk.marker_location_accuracy respectively. This value appears in the Reference pane settings dialog.
In case you would like to set the individual accuracy for certain camera or marker, you should assign the three-component vector to camera.reference.location_accuracy or marker.reference.accuracy. For example:
camera.reference.location_accuracy = Metashape.Vector([1, 1, 1]) # one meter accuracy for all coordinates
marker.reference.accuracy = Metashape.Vector([0.1, 0.1, 0.5]) # ten cm accuracy for XY and 50 cm for altitude