Matt Allington shows how you can use M to rename all columns at once in a table in Power Query:
When you are using a matrix like this, it can be difficult to tell which “Year” column is coming from which table, as shown below.
One solution to this problem is to rename all the columns in each table by pre-pending Order or Delivery to the front of the existing column names. Once that is done, it is much clearer which column is which.
Matt describes the concept for you, but also has a video showing how to do this.