In Numbers how do I add a Header Row after the spreadsheet is created?

On a few occasions, I have inadvertently created a worksheet in Numbers without first creating a true Header Row (this usually happens when I copy and paste from another table and accidentally paste the values into the top left-hand corner -- where the header should start). When I attempt to add a row above my incorrect "Header Row" so that I can create the true Header Row, I discover that there are no options available to me. Under "Table" -- the "Add Row Before" option is grayed out (not available), although I could chose to "Add Row Below" (but that is not what I want). Under this same menu item, there is a "Delete Header Row" but no option to "Add Header Row."

What am I missing? This surely is a simple task to add a row at the top of a worksheet to create a Header...right?

Thank you!

Scott