Begin by logging into your ConvertKit account. Navigate to the subscribers section and export your subscriber data. ConvertKit typically allows you to export data in CSV format. Ensure you have the export file saved on your local machine.

Ensure MongoDB is installed on your local machine or server where you intend to import the data. Additionally, install MongoDB tools which include `mongoimport`, a command-line utility to import data into MongoDB. You can download these from the MongoDB official website.

Open your exported CSV file and clean it up if necessary. Ensure that headers are correctly labeled and that there are no corrupt or missing fields. The file should be in a consistent format that MongoDB can recognize and import.

Since MongoDB uses BSON (Binary JSON) format, convert your CSV file to JSON. You can write a simple script using Python or another scripting language to achieve this. For example, using Python's `pandas` library:

```python
import pandas as pd

csv_file = 'path_to_your_convertkit_export.csv'
json_file = 'output.json'

df = pd.read_csv(csv_file)
df.to_json(json_file, orient='records', lines=True)
```

Launch the MongoDB shell by running `mongo` in your terminal. Create a new database and collection where you will import your data. For example:

```shell
use convertkitData
db.createCollection("subscribers")
```

Use the `mongoimport` tool to import the JSON file into your MongoDB database:

```shell
mongoimport --db convertkitData --collection subscribers --file output.json --jsonArray
```

Ensure the `convertkitData` database and `subscribers` collection match those you created in the previous step.

After running the `mongoimport` command, verify that the data has been correctly imported into MongoDB. Use the MongoDB shell to query the database:

```shell
use convertkitData
db.subscribers.find().pretty()
```

Check to ensure all records are present and correctly formatted within the MongoDB collection.

By following these steps, you can manually move data from ConvertKit to MongoDB without relying on external integrations or connectors.