Using JMP 16.2 on Windows 11 I created a spreadsheet
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With the A1 value (Header) merged and centered across A1-B1.
Using the Excel Wizard, I simply specified the Column Headers starting in row 1 and the Number of rows with column headers as 2 and finally the Data Starts on row 3
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Clicking on the Import button I got
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I have attached the Excel file. Try using it and see if you get what I got.
Jim