Вы можете использовать XLSX.utils.aoa_to_sheet
для добавления заголовка.
Например:
// Do mind! it is array of array
var Heading = [
["FirstName", "Last Name", "Email"],
];
var Data = [
{firstName:"Jack", lastName: "Sparrow", email: "abc@example.com"},
{firstName:"Harry", lastName: "Potter", email: "abc@example.com"},
];
var ws = XLSX.utils.aoa_to_sheet(Heading);
XLSX.utils.sheet_add_json(ws, Data);
ref: https://docs.sheetjs.com/#array-of-arrays-input