Hi, thanks for explaining the issue. Copilot edits the current workbook only when you open the file in a supported Excel app with an active Copilot license and cloud storage enabled.
When those conditions do not apply, Copilot creates a new file instead of changing your sheet. You must open the workbook, select the data, then use Copilot to add formulas, create columns, or format ranges directly in the same file after you review and apply the changes.