Hi P. Prasath.,
That answer is a bit old (over 10 years) and a lot has changed since then. In Highcharts v2.1.9 the zoom method wasn't assigned to the "chart" object, so a small customization of the highcharts.src file was required.
Now, it's a documented method stored on a chart.prototype and you can use it out of the box without a need of editing any Highcharts source files.
API Reference: https://api.highcharts.com/class-refere ... rt#zoomOut
Demo: https://jsfiddle.net/BlackLabel/wLucyb4v/
Best regards!