how can you change the tap position of a Three-Phase OLTC Regulating Transformer (Phasor Type) programmatically?

i used this command: set_param('dataGather_w_con/Autotransformer','Initial tap position','4'). I tried to change 'Initial tap position' to 'Initialtapposition', to 'Initial_tap_position', and to 'tap' but it doesn't work still. Thanks to everyone who helps.