Excel, reference header row instead of column in xlookup formula?

I need to make an Excel spreadsheet template that merges customer data from two other Excel files that are downloaded from a vendor application each morning. The files have a customer ID number for a primary key so I use XLOOKUP to pull data from other columns in the row with the customer ID.

The problem is the columns are not always in the same order on the downloaded reports. For example, in one file, "LastName" is usually but not always column B. This morning it was column K. But row 1 is always "LastName" regardless of what column it ends up in. So my question...

How do I reference the row 1 value in my XLOOKUP formula instead of the column letter?