Hi NishiMura,

Use below code snipped  for different "tooltip" for each graph 

tooltip: {
    shared: false,
    formatter: function() {
        var text = '';
        if(this.series.name == 'count') {
            text = this.x + ': ' + this.series.name +
                   '<br> $' + Highcharts.numberFormat(this.y, 0);
        } else {
            text = 'In ' + this.x + ' the median value was' + this.series.name +
                   'and the total $' + Highcharts.numberFormat(this.y, 0);
        }
        return text;
    }
}

Below is the working URL and attached oml

https://dbaghel.outsystemscloud.com/testChart/screen?_ts=637865246760686903

Hope this will help you.

Best Regards

Devendra