WordPress Membership Plugin
I managed to make it work
Below is the change I made for those who have the same problem
————————
arquivo classes/class.bMembers.php
if (isset($_POST['s'])){
$query .= " WHERE user_name LIKE '%".addslashes($_POST['s'])."%'
OR first_name LIKE '%".addslashes($_POST['s'])."%'
OR last_name LIKE '%".addslashes($_POST['s'])."%'
OR email LIKE '%".addslashes($_POST['s'])."%'";
}