Based on what I know:

1. If you didn't like the food the first think you usually ask for is a "book of complaints".
2. Either manager or administrator can be a good a choice if wish to speak to them.

• Please, let me speak/talk to you manager (administrator) - If you are simply unsatisfied
• Would you be so kind as to call (for) the manager (administrator) - Somewhat very formal
• I wish (would like) to speak/talk to the manager (administrator) - If you are really dissatisfied

3. I, personally, wouldn't use the word supervisor as it mostly addresses the manager of a manager, the person who supervises the work of a manager and assists him in directing and organizing the staff. However, it is a possible word too.
4. If there is something wrong with your dish you may call the waiter "Excuse me" and ask him to change it.
5. In most cases if you politely speak to the wait staff they'll handle everything.

Be cautious and avoid slang and bad words when addressing the staff.

Based on what I know:

1. If you didn't like the food the first think you usually ask for is a "book of complaints".
2. The word manager is a good a choice if wish to speak to someone who manages the restaurant.

• Please, let me speak/talk to you manager - If you are simply unsatisfied
• Would you be so kind as to call (for) the manager - Somewhat very formal
• I wish (would like) to speak/talk to the manager - If you are really dissatisfied

3. I, personally, wouldn't use the word supervisor as it mostly addresses the manager of a manager, the person who supervises the work of a manager and assists him in directing and organizing the staff. However, it is a possible word too.
4. If there is something wrong with your dish you may call the waiter "Excuse me" and ask him to change it.
5. In most cases if you politely speak to the wait staff they'll handle everything.

Be cautious and avoid slang and bad words when addressing the staff.