@paulfansare,
You can render chart with dataPoints based on the values being selected from dropdown using change event. Below is the code-snippet for the same.
$(".dropdown").change(function() {
chart.options.data[0].dataPoints = [];
var e = document.getElementById("dd");
var selected = e.options[e.selectedIndex].value;
dps = jsonData[selected];
chart.options.title = { text: "Chart with " + selected };
for(var i in dps) {
var xVal = dps[i].x;
chart.options.data[0].dataPoints.push({x: new Date(xVal), y: dps[i].y});
}
chart.render();
});
Please take a look at this JSFiddle for complete code.

But i am facing an issue, i want to add data series using a multiselect dropdown,
It would be helpful for us to understand your issue better when we look at your code working live in jsfiddle. So I request you to create jsfiddle reproducing the issue and share it with us.
—
Vishwas R
Team CanvasJS