WooCommerce - Adjust the default quantity

functions.php

// Simple products
add_filter( 'woocommerce_quantity_input_args', 'jk_woocommerce_quantity_input_args', 10, 2 );

function jk_woocommerce_quantity_input_args( $args, $product ) {
	if ( is_singular( 'product' ) ) {
		$args['input_value'] 	= 2;	// Starting value (we only want to affect product pages, not cart)
	}
	return $args;
}