Connecting two different 'user' tables into one single table
Option 1: Single table

If you don't really have a lot of unique columns that belong only in tb_student or in tb_teacher, then it might make sense to combine everything in the tb_user table, and there would be no need for the tb_teacher and tb_student tables. They would be superfluous. But there could be reasons for keeping them separate, like maybe relationships to the other tables in your schema. 

Option 2: Normalisation

So if you try to follow the principles of normalisation, and keep three separate tables, then all columns that are unique to the tb_student tables should be found only there, and likewise with the tb_teacher table. (You don't have anything unique to the tb_teacher table at the moment, but maybe you'll think of something later?) You will need to add a column e.g. id_tb_user in each of the tb_student and tb_teacher tables, and declare foreign key constraints for these columns referring to the tb_user table. E.g.:

CREATE TABLE tb_teacher (
...
  id_tb_user int unsigned,
...
  CONSTRAINT tb_teacher_fk1 FOREIGN KEY (id_tb_user)
    REFERENCES tb_user(id_user)
...
)


The tb_user table will contain all the shared columns: name, status and some of the other columns you already have, but not entry_year.

To retrieve information about students, including info about them in the tb_user table, you will then use a query with a simple INNER JOIN:

SELECT s.id_student, 
  s.entry_year, 
  u.username, 
  u.name -- + any other columns you want
FROM tb_student s
  INNER JOIN tb_user u ON s.id_tb_user = u.id_user
WHERE 
  u.username = 'spectrum@unida.gontor.ac.id'; 
  -- or any other condition you want


(To retrieve info about students and teachers in a single query, use instead two LEFT OUTER JOINs.)

By the way, you should also explicitly declare your primary keys as such. It's also a good idea to use int unsigned as the data type for these columns (or even bigint unsigned, although that is rarely needed), and it's also often a good idea to use auto_increment (see also the FAQ) so that MariaDB/MySQL does the job of generating a new id when you insert a new row: 

CREATE TABLE tb_user (
    `id_user` int unsigned auto_increment PRIMARY KEY,