Begin by cloning the GitHub repository that contains the data files you wish to move to Apache Iceberg. Use the `git clone` command with the repository URL to download it to your local machine. This allows you to work with the data files directly.

```bash
git clone https://github.com/yourusername/your-repo.git
```

Navigate into the cloned repository directory and identify the data files you intend to move. Ensure these files are in a format supported by Apache Iceberg (e.g., CSV, Parquet, Avro). If necessary, convert the files to a supported format using a script or command-line tool.

```bash
cd your-repo
# Convert or prepare files here if needed
```

Set up Apache Iceberg on your local environment. Install Apache Iceberg and any dependencies required to run it, such as Apache Spark or Flink, depending on your processing needs. You can do this using package managers like pip for Python or maven for Java.

```bash
# Example for Spark with Iceberg
pip install pyspark
pip install iceberg-spark-runtime
```

Configure an Iceberg catalog to manage your tables. This involves setting up a metastore (such as Hive Metastore) or using a file-based catalog. Define the catalog properties in your Spark or Flink configuration.

```python
spark.sql("CREATE CATALOG my_catalog USING 'hive'")
```

Use Spark or Flink to read the data files and write them into an Apache Iceberg table. Create a DataFrame from your data files, apply any necessary transformations, and then write the data to an Iceberg table using the configured catalog.

```python
df = spark.read.format("csv").option("header", "true").load("path/to/datafile.csv")
df.write.format("iceberg").save("my_catalog.my_db.my_table")
```

Once the data is written, verify that it was successfully transferred to Iceberg by querying the table. Use Spark SQL or Flink SQL to run a few basic queries and ensure the data looks as expected.

```python
spark.sql("SELECT FROM my_catalog.my_db.my_table").show()
```

After verifying the data, clean up any temporary files or configurations you no longer need. Document the process you followed, including any scripts or commands used, to ensure reproducibility and ease of future data migrations.

```bash
# Remove any temporary files
rm -rf /path/to/temporary/files
```

By following these steps, you can effectively move data from a GitHub repository to an Apache Iceberg table without relying on third-party connectors or integrations.