If you will go through the documentation, wc_memberships_get_user_memberships() returns a list of WC_Memberships_User_Membership objects. WC_Memberships_User_Membership class has a get_end_date() method that will give the expiry date. You can proceed like this
// Get memberships for the current user.
$memberships = wc_memberships_get_user_memberships();
// Verify that they have some memberships.
if ( $memberships ) {
foreach( $memberships as $memberships ) {
// Print the expiration date in mysql format.
echo $membership->get_end_date();
}
}