Redefining an existing Table Schema for Foreign Key Constraint - Question

Hello everyone,

I am new to the forum and fairly new to databases (particularly PostgreSQL).
I have done some searching on the internet and can't really get a hold of an
answer to my question. So here it goes:

I am working on a Customer Purchasing-based project where I must use a
database with existing customer data. The database currently follows the
following schema for two tables:

Creditcards Table
id:integer -- primary key
credit_card_number:varchar(16)
name_on_card:varchar(100)
expiration:date

Customers Table
id:integer -- primary key
first_name:varchar(50)
last_name:varchar(50)
credit_card_number:varchar(16)
address:varchar(200)
email:varchar(50)
password:varchar(20)

Currently, the database contains thousands of records in the Customers and
Creditcards tables. I would like to re-define the Customers table to follow
the following schema:

Customers Table
id:integer -- primary key
first_name:varchar(50)
last_name:varchar(50)
cc_id:integer references Creditcards.id
address:varchar(200)
email:varchar(50)
password:varchar(20)

As you can see, I would like to convert the column that used to be
"credit_card_number" from the Customers table and turn it into a "cc_id"
which is an integer that references the column "id" from the table
Creditcards.

I would like for the Customers.cc_id to match with a Creditcards.id that has
the same credit_card_number.

Does anyone know of a script that I can use to do this? Am I supposed to use
Triggers? How can this be done safely. I would like for the data to be
consistent. Thank you guys in advance.
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