Yes, you can add a trial balance to an existing workpaper.
The Trial Balance page will be available regardless of whether a trial balance has been added. At the top of this page, you’ll see two options for adding or updating the trial balance:
Update - Use this option to manually upload a trial balance in CSV format. Ensure your CSV meets the required format by referring to this article.
Switch to Xero - If the entity is linked to a Xero file, this option will appear. Clicking it will pull the trial balance directly from Xero.
