WHMCS 6 Upgrade: Converting a multi-dimensional $this->_tpl_vars to the new parameter $template->getVariable

I encountered a problem when I upgraded WHMCS 5 to WHMCS 6 on one of my custom templates.

One of the template migration instructions for PHP blocks as stated HERE is below:

EXAMPLE:

{php}

// Retrieve a single template variable. 
$myValue = $this->_tpl_vars['myVariable'];

// Loop through all template variables.
foreach ($this->_tpl_vars as $key => $value) {
   echo "{$key}: {$value}";
}

// Assign a new template variable.
$this->assign('myNewVariable', 'myNewValue');

{/php}

Converts to:

{php}

// Retrieve a single template variable. 
$myValue = $template->getVariable('myVariable')->value;

// Loop through all template variables. 
foreach ($template->getTemplateVars() as $key => $variable) {
   echo "{$key}: {$variable->value}";
}

// The assign() method works as it did before, though it must now be 
// called on the $template object instead of $this.
$template->assign('myNewVariable', 'myNewValue');

{/php}

Now the problem is this. How will I convert a multi-dimensional $this->_tpl_vars ? Or to be more specific, how will I convert a code that looks like this:

$email = $this->_tpl_vars['clientsdetails']['email'];

I was looking at the new $client Object, but not sure how to use it either and how to retrieve the email info from it.

Hope anybody can help me. Thanks!