I am not sure which part of the height you are referring to, so I estimate that you are talking about the distance between the camera and the floor version, this setting is adjustable:

//1::
viewer.loadExtension( 'Autodesk.BimWalk', { cameraDistanceFromFloor: 1.0 } );

//2: BimWalk :
var bimWalkExt = viewer.getExtension( 'Autodesk.BimWalk' );
bimWalkExt.set( 'cameraDistanceFromFloor', 1.0 );

//3: Viewer :
var config3d = {
    cameraDistanceFromFloor: 1.0,
    extensions: [ 'Autodesk.BimWalk' ]
};

var viewer = new Autodesk.Viewing.Private.GuiViewer3D( container, config3d );

I hope this is helpful to you!