Use a filter to adjust the content of the user page that is created with PMPro and the User Pages addon.

pmpro-user-page-content-filter.php

<?php
/*
	When the user page is created, add some content.
*/
function my_pmpro_user_page_purchase_postdata_content($postdata, $user, $level)
{
	//update post content
	$postdata['post_content'] = "<p>Thank you for using our site.</p>

			<p>This is some extra content for the user page.</p>

			<p>We got links:</p>
			<ul style='margin-bottom: 3em;'>
			<li><a href='" . home_url() . "'>Homepage</a></li>
			<li><a href='" . home_url("/members/") . "'>Members Area</a></li>
			<li><a href='" . home_url("/contact/") . "'>Contact Us</a></li>
			</ul>";

	return $postdata;
}
add_filter("pmpro_user_page_purchase_postdata", "my_pmpro_user_page_purchase_postdata_content", 10, 3);
?>

This recipe is included in the blog post on "Setting Default Page Content or Page Template with the User Pages Add On" at Paid Memberships Pro here: https://www.paidmembershipspro.com/setting-the-default-page-content-or-page-template-with-the-user-pages-add-on/

I have forked this to allow for multiple levels
https://gist.github.com/kimwhite/5e16208b33a725422203798c499c63b9