Import and Export using a flat file is the easiest option. You can use CSV file if it is a onetime activity. However, If you think it is a repetitive activity then I would suggest you use HANA ETL options like HANA SLT replication, Smart Data access, etc.
SAP HANA Replication allows migration of data from source systems to SAP HANA database. Simple way to move data from existing SAP system to HANA is by using various data replication techniques.
System replication can be set up on the console via command line or by using HANA studio. The primary ECC or transaction systems can stay online during this process. We have three types of data replication methods in HANA system -
For more details, you can refer to our site on SAP HANA Data Replication.