Add “Loser” to mailing list (Brevo) and send email

Hello people
am new here in the forum and PHP and JavaScript developer. I am currently customizing the plugin according to the requirements for my employer.

We want to send an email when the user lost and still add to the mailing list.

Can anyone tell me what function in frontend/frontend.php is called for this when the user has lost?

Otherwise, is there any other way to implement this feature without programming effort?

The request is urgent because the day after tomorrow we will send out the newsletter for the competition with the great wordpress Lucky Wheel plugin to our customers.

Thanks in advance and greetings from the beautiful Lake Lucerne