It looks like you're using the Timeline app, the documentation is found here for simpleXML options:
https://docs.splunk.com/Documentation/Timeline/1.1.0/TimelineViz/TimelineXML
it doesn't look like you can add other fields.
There is a Gantt Chart app found here: https://splunkbase.splunk.com/app/1741/ that can be customized.
the simpleXML would look something like (the search is a post-process called demo_search1):
<row>
<panel>
<title>Tool Lifecycle</title>
<html encoded="1"><h2>Gantt Chart</h2>
<div id="demo-view" class="splunk-view" data-require="app/gantt/components/gantt/gantt" data-options="{
&quot;managerid&quot;: &quot;demo_search1&quot;,
&quot;startField&quot;: &quot;_time&quot;,
&quot;durationField&quot;: &quot;duration&quot;,
&quot;categoryLabel&quot;: &quot;ScriptName&quot;,
&quot;categoryField&quot;: &quot;ScriptName&quot;,
&quot;seriesLabel&quot;: &quot;SecondScriptName&quot;,
&quot;seriesField&quot;: &quot;ScriptName2&quot;,
&quot;extrasField&quot;: &quot;anyExtraField&quot;,
&quot;compact&quot;: &quot;true&quot; }">
</div></html>
</panel>
</row>
