Usage:
add_filter( 'arm_add_new_optin_settings', 'your_function', 10, 2);
function your_function($content, $email_settings) {
    //$content Email Tool Options HTML.
    //$emailTools Email Tool Settings.
    $content = "Add Your Options HTML Here.";
	return $content;
}
Parameters:
$content
Email Tool Options HTML
$emailTools
Email Tool Settings
Usage:
add_filter( 'arm_get_optin_settings', 'your_function', 10, 2);
function your_function($email_tools, $email_settings) {
    //$email_tools Email Tools Settings.
    //$email_settings All Email Settings.
    $email_tools['some_tool'] = array();
    return $email_tools;
}
Parameters:
$email_tools
Email Tools Settings
$email_settings
All Email Settings
Usage:
add_filter( 'arm_change_optin_settings_before_save', 'your_function');
function your_function($email_tools) {
    //$email_tools Email Tools Settings.
    $email_tools['some_tool'] = array();
    return $email_tools;
}
Parameters:
$email_tools
Email Tools Settings