A monthly export might have Asset, Location, January and February columns. That is convenient for reading across a page, but a downstream report may need one record per asset and month. Define that record before reshaping the table: Asset and Location identify it, Month names the observation, and Quantity holds its value.

Use a copy of the workbook and retain the original export. In a small example, give two assets a quantity in each of two months. The expected result contains four asset-month observations. Write those four expected combinations down so a plausible-looking preview cannot conceal a missing identifier.

Select what should remain as columns

In Power Query Editor, select the stable identifier columns, using Ctrl for multiple selections, then choose Transform, Unpivot Columns, Unpivot Other Columns. This retains the selected columns and turns the others into Attribute and Value pairs. Rename those output columns for their meaning. Microsoft documents that Other includes newly introduced columns on refresh; Unpivot Only Selected Columns instead confines the operation to its explicit selection.

Inspect every row in the small result. January for the first asset must still carry that asset's location, and its quantity must match the original intersection. A larger row count is expected here because the meaning of a row has changed.

Test the next export's shape

Add March with a known quantity to the disposable source and refresh the query. Confirm that March appears as a month value for each relevant asset. Check the quantity and identifier together, rather than checking only that the word March appears somewhere.

Then consider an export that also adds a Supervisor column. Under an Other rule, that unselected column is another candidate for reshaping. Decide which fields are identifiers and keep the export schema under review; a rule that welcomes future months cannot independently recognise unrelated metadata.

Before using the output, remove temporary test data and inspect the actual month values for unexpected labels. Keep the retained-column list with the workbook so the next maintainer knows why those fields remain fixed while the reporting periods become rows.

Sources: Microsoft: unpivot columns.