Start by exporting the data you need from Retently. Log into your Retently account, navigate to the data or reports section, and look for an option to export data. Choose a suitable format like CSV or JSON for easy handling. Download the exported file to your local system.

Prepare your local environment for data processing. Ensure you have Python installed, as it will be used to transform and load the data. Install necessary Python packages, like `pandas` for data manipulation and `pymongo` for MongoDB interaction, using pip:
```bash
pip install pandas pymongo
```

Write a Python script to read the exported data file and transform it to fit your MongoDB schema requirements. For example, you can use pandas to load a CSV file and then reformat or clean the data as needed:
```python
import pandas as pd

# Load the data
data = pd.read_csv('retently_data.csv')

# Perform any necessary transformations
# e.g., renaming columns, converting data types
data['new_column'] = data['old_column'].apply(some_transformation_function)
```

Set up a MongoDB database where the data will be stored. Ensure MongoDB is installed and running on your local machine or a server. Create a database and collection if they do not already exist:
```bash
mongo
use my_database
db.createCollection('my_collection')
```

Use the `pymongo` library in your Python script to connect to your MongoDB instance. Set the connection string according to your MongoDB setup (local or remote):
```python
from pymongo import MongoClient

client = MongoClient('mongodb://localhost:27017/')
db = client['my_database']
collection = db['my_collection']
```

Convert the transformed data into a format suitable for MongoDB (e.g., a list of dictionaries if using pandas) and insert it into the desired collection:
```python
# Convert DataFrame to dictionary
data_dict = data.to_dict('records')

# Insert data into MongoDB
collection.insert_many(data_dict)
```

Check that the data has been successfully transferred by querying your MongoDB collection. This can be done using either the MongoDB CLI or a Python script:
```python
# Verify insertion
for document in collection.find():
print(document)
```
Alternatively, use the MongoDB shell:
```bash
mongo
use my_database
db.my_collection.find().pretty()
```

By following these steps, you can effectively move data from Retently to a MongoDB destination without relying on any third-party connectors or integrations.