[Solved]-How can I set the units on multiple axis on Highcharts-Highcharts

You need to only format the second y-axis labels:

    yAxis: [{...}, {
        ...,
        labels: {
            formatter: function() {
                return 3.3 / 4096 * this.value
            }
        }
    }]

Live demo: http://jsfiddle.net/BlackLabel/gbhe64n1/

API Reference: https://api.highcharts.com/highcharts/yAxis.labels.formatter