Hello Govind
System will pick the functional area with Restrict to as blank.
If you have not maintained this entry for a specific G/L Account and only restrict to the Sales Object and Non-Sales Objects are maintained.
In this case, system will pick the default functional Area.
Additionally,there is an option to Manually Enter G/L balances in the Migration of Accounting Transaction data. You can manually enter the functional area here but it is not an excel upload.
Thanks
Parveen Kumar