No, andara creates automatically an Excel file with the dashboard structure you design in andara app in the Edit mode. This Excel file will be automatically placed and stored by the app in your box.com account. This is the only Excel file synced with andara. Therefore, you CAN NOT link any Excel file of your choosing to andara.
Also, the structure of the dashboard can only be designed and edited in andara. The Excel file will be changed automatically based on the changes to the structure you do in the andara app. The Excel file can only be used to introduce or edit data values.