A query is a list of steps, and you can change any of them later.
- Select the X next to a step in Applied Steps to delete it.
- Select the gear next to a step to reopen its dialog, or change its formula in the formula bar.
- Rename the query in Query Settings > Name. Other queries and Excel refer to it by this name.
Changing an early step can break a later one. The classic case: a step renames Qty to Quantity, and a later step still asks for [Qty]. Power Query then shows Expression.Error: The column 'Qty' of the table wasn't found. Select the failing step, read the error, and update the name it uses.