[Fixed]-How to change a field of fullcalendar io through html?

You could use a data attribute on the div to pass a configurable height:

<div id="calendar_dash" data-height="{{ calendar_height }}"></div>

… where calendar_height is an integer that you have passed to the template context.

Then in your JS:

var calendar_div = $('#calendar_dash');

calendar_div.fullCalendar({
    // ...
    height: calendar_div.data("height"),
    //...
});

You may want to enhance this a bit to fall back to some default if the data attribute is not specified.