First, clone the GitHub repository containing the data to your local machine. Use the `git clone` command followed by the repository URL. This will create a directory with the repository's contents on your local system.

```bash
git clone https://github.com/username/repository.git
```

Navigate into the cloned repository directory. Identify and extract the data files you need to move. Ensure these files are in a format that Apache Iceberg can handle, such as CSV, Parquet, or JSON.

```bash
cd repository
```

Set up an environment where you can run Apache Iceberg. This typically involves installing Apache Spark or Apache Flink, as Iceberg works with these engines. Ensure you have Java and the respective framework installed and configured.

```bash
# Example for installing Spark
brew install apache-spark
```

Configure a catalog for your Iceberg tables. This can be done using a Hive Metastore, AWS Glue, or a JDBC catalog. Set up the catalog configuration in your Spark or Flink environment to specify where your Iceberg metadata will be stored.

Use Spark or Flink to read the extracted data files and write them into an Iceberg-compatible format. This involves loading the data into a DataFrame or Dataset and using the Iceberg API to write it to a table.

```python
from pyspark.sql import SparkSession

spark = SparkSession.builder \
.appName("IcebergDataTransfer") \
.config("spark.sql.catalog.my_catalog", "org.apache.iceberg.spark.SparkCatalog") \
.config("spark.sql.catalog.my_catalog.type", "hive") \
.config("spark.sql.catalog.my_catalog.uri", "thrift://localhost:9083") \
.getOrCreate()

df = spark.read.csv("path/to/datafile.csv")
df.write.format("iceberg").mode("overwrite").save("my_catalog.my_namespace.my_table")
```

After writing the data to Iceberg, verify that it has been correctly transferred. Use Spark or Flink to query the Iceberg table and check if the data is accurate and complete.

```python
result = spark.sql("SELECT FROM my_catalog.my_namespace.my_table")
result.show()
```

After successfully transferring the data to Apache Iceberg, clean up your local environment. This includes removing the cloned GitHub repository and any temporary files used during the transfer process to free up space and maintain organization.

```bash
rm -rf repository
```

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