Begin by logging into your LinkedIn Ads account. Navigate to the Campaign Manager and select the campaign or data set you wish to export. LinkedIn allows you to export campaign data manually. Choose the "Export" option to download the data in a CSV format, which is typically the most convenient format for data manipulation and importation into databases.

Open the exported CSV file using a spreadsheet application like Microsoft Excel or Google Sheets. Review the data to ensure it is complete and accurate. Clean the data by removing any unnecessary columns, correcting formatting issues, and handling any missing values. This step is crucial to ensure the data is ready for import into PostgreSQL.

Ensure that you have a PostgreSQL database server running. You can set this up on your local machine or a remote server. If needed, install PostgreSQL following the official installation instructions for your operating system. After installation, use the `psql` command-line tool or a GUI like pgAdmin to create a new database and define the necessary tables that correspond to the structure of your LinkedIn Ads data.

Convert your cleaned CSV data into a format suitable for PostgreSQL import. This typically involves ensuring that the data types in your CSV match the data types of your PostgreSQL table columns. Save the adjusted file in a CSV format again, ensuring that the delimiter used in the file matches what PostgreSQL expects (commonly a comma).

Use SQL commands to create a table in your PostgreSQL database that matches the structure of your CSV file. Define each column with the appropriate data type. Here is an example SQL command to create a table:
```sql
CREATE TABLE linkedin_ads_data (
campaign_name TEXT,
impressions INTEGER,
clicks INTEGER,
spend NUMERIC,
date DATE
);
```

Use the `COPY` command in PostgreSQL to import the CSV data into your table. This command reads from the CSV file and inserts the data into the specified table. Here is an example command:
```sql
COPY linkedin_ads_data(campaign_name, impressions, clicks, spend, date)
FROM '/path/to/your/file.csv'
DELIMITER ','
CSV HEADER;
```
Ensure the file path is correct and accessible by the PostgreSQL server.

Once the data has been imported, verify the import by querying the PostgreSQL table. Use a simple `SELECT` statement to ensure that the data appears as expected and there are no discrepancies. Here is an example query:
```sql
SELECT * FROM linkedin_ads_data;
```
Check for errors or issues, and ensure the data integrity is maintained. If there are any issues, you may need to revisit the data cleaning or table setup steps.

By following these steps, you can manually transfer data from LinkedIn Ads to a PostgreSQL database without relying on third-party connectors or integrations.