https://docs.oracle.com/javase/8/javafx/api/javafx/concurrent/Service.html
1) "manging" should be "managing"

https://docs.oracle.com/javase/8/javafx/api/javafx/concurrent/Task.html
2) "lets" should be "let's"
3) the line
customer.setF setFirstName(rs.getString("FirstName"));
should be
customer.setFirstName(rs.getString("FirstName"));