[Solved]-Highcharts tooltip date format when using pointFormat-Highcharts

you should modify the tooltip header format

tooltip: {    
    xdateformat: '%b %y'
}

or if you want to modify the whole html

tooltip: {    
    headerformat: '<b>{point.key:%b \'%y}</b><br>'
}

use html in tooltip and format using dateformat

highcharts.dateformat(%y-%m,this.x)

just change your point.x: format string from {point.x:%y-%m} to {point.x:%b-%y} as shown bellow

tooltip: {
        headerformat: '<span style="font-size:10px">{point.x:%b-%y}</span><table>',
        pointformat: '<tr><td style="color:{series.color};padding:0;font-size:11px;">{series.name}: </td>' +
        '<td style="padding:0"><b>{point.y:,.0f}</b></td></tr>',
        footerformat: '</table>',
        shared: true,
        usehtml: true
    },