Insert data into a particular field of a table

[system]

I have created a database and a table inside with the following column names
id
username
password
score

Using the signup form I’m able to add new ids, usernames and passwords to the table.
Now when a user logs in I’m able to check with the table whether the username and password is correct and allow the user to log in and take a quiz. Now comes my question. How can I store the result of the quiz to ‘score’ field associated with that particular ‘username’ and ‘password’?
When I give the INSERT INTO code it creates a new row in the table rather than saving it in the score field of that particular username and password! PLEASE HELP!

[m11]

You would want to UPDATE not INSERT

For example:

UPDATE the_table SET score = the_score WHERE username = ‘the_username’