How to populate choice filed value based on other field

[seenu_pvr]

Dear Friends,

I have a on change client script where I need to populate the channel field as self service when the caller id role is ITIL. but I cant populate the channel field as self servcie. please advise. Here is the On change script.

function onChange(control, oldValue, newValue, isLoading, isTemplate) {

    if (isLoading || newValue === '') {

        return;

    }

    var gr = new GlideRecord('sys_user_has_role');

    gr.addQuery('user.sys_id', newValue);

    gr.addQuery('role.name', 'itil');

    gr.query();

    //g_form.addInfoMessage(newValue);

    if (gr.next()) {

        g_form.getOption('contact_type', 'self-service');

       // g_form.addInfoMessage("iam in if loop");

    } else {

        g_form.getOption('contact_type', 'None');

       // g_form.addInfoMessage("I am in else loop");

    }