[Solved]-Change first tick label on yAxis-Highcharts

You can define your own yAxis.tickPositioner to define all positions where you wish a tick should be placed.

Since in your case you don't want to override the entire behavior, but just place a tick at the min position, you can leverage the axis.getLinearTickPositions(interval, min, max) method to get the array of default positions that would be otherwise generate, and then append your additional ticks to this array.

The code below has ticks added on both the min and max of the y-axis

yAxis: {
    showFirstLabel: true,
    showLastLabel: true,
    tickPositioner: function(min, max) {
        // specify an interval for ticks or use max and min to get the interval
        var interval = Math.round((max - min) / 5);
        var dataMin = this.dataMin;
        var dataMax = this.dataMax;
        // push the min value at beginning of array
        var positions = [dataMin];
        var defaultPositions = this.getLinearTickPositions(interval, dataMin, max);
        //push all other values that fall between min and max
        for (var i = 0; i < defaultPositions.length; i++) {
            if (defaultPositions[i] > dataMin && defaultPositions[i] < dataMax) {
                positions.push(defaultPositions[i]);
            }
        }
        // push the max value at the end of the array
        positions.push(dataMax);
        return positions;
    }
}

Show tick on min and max of y axis | Highchart & Highstock @ jsFiddle
Demo of your chart @ jsFiddle