Hey!
Thanks for reaching out, this is something more related with WordPress rather than the Events Calendar Plugin, but you can add a new link to logout from the account in your current theme as follows:
<?php if ( is_user_logged_in() ) : ?>
<a href="<?php echo wp_logout_url(); ?>">Logout</a>
<?php endif; ?>
This will only display a Logout link if the user is logged in, you can add this snipped of code on the template you would like to display the link, and add custom CSS class to edit to match your style guide.
Please let me know if you have any other questions about this issue or if there is anything else I can do for you.
Thanks,
Crisoforo