Begin by logging into your ConvertKit account. Navigate to the subscribers or other data sections you wish to transfer. Use the export functionality provided by ConvertKit to download the data as a CSV file. This file will contain all the necessary information needed for the migration to PostgreSQL.

Open the CSV file in a spreadsheet editor like Microsoft Excel or Google Sheets. Review the data to ensure it is clean and correctly formatted. Make any necessary adjustments, such as removing unnecessary columns or renaming headers to match the schema of your PostgreSQL database.

Install PostgreSQL on your local machine or set up a PostgreSQL instance on a server. Make sure you have the necessary permissions to create databases and tables. Use the PostgreSQL interactive terminal (psql) or another SQL client to create a new database and table(s) matching the structure of your CSV data.

Define the schema for the table(s) into which you will import the data. Use SQL commands to create tables with appropriate data types for each column. Ensure that the table structure aligns with the CSV file. For example:
```sql
CREATE TABLE subscribers (
id SERIAL PRIMARY KEY,
email VARCHAR(255),
name VARCHAR(255),
created_at TIMESTAMP
);
```

Ensure you have installed PostgreSQL command-line tools such as `psql` or a GUI tool like pgAdmin. These tools will allow you to interact with your PostgreSQL database and facilitate data import operations.

Use the PostgreSQL `COPY` command or a similar function to import data from the CSV file into the PostgreSQL table. For example, using `psql`:
```bash
\COPY subscribers(email, name, created_at) FROM 'path/to/your/file.csv' DELIMITER ',' CSV HEADER;
```
Ensure that the path to the CSV file is correct and that the file is accessible. The `CSV HEADER` option indicates that the first row of the file contains column headers.

After importing the data, verify its integrity and consistency. Run SQL queries to check that all records were imported correctly and that there are no discrepancies between the original CSV data and the PostgreSQL table. Perform random checks on a few records to ensure accuracy. If necessary, write additional scripts to handle any data anomalies or transformations needed post-import.