If you want to override modules you have to create an extension. If you see url address chat/startchat there is 99% chance that module file is located in
if you want to override this module you have in your extension have this structure
module.php file content should the following
$Module = array( "name" => "Start chat overide");
$ViewList = array();
$ViewList['startchat'] = array(
'script' => 'startchat.php',
'params' => array()
startchat.php file content can be just copied from modules/lhchat/startchat.php file. I suggest just look at customstatus extension as example. There is overriden user/login file.
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