How about this:

Table:
LOAD
	ID,
	Name,
	Age,
	Gender
FROM [lib://Desktop/TESTING.xlsx]
(ooxml, embedded labels, table is Sheet1);


FOR EACH SheetName IN 'Sheet2', 'Sheet3'
LOAD
	A AS ID,
	B AS Name,
	C AS Age,
	D AS Gender
FROM [lib://Desktop/TESTING.xlsx]
(ooxml, no labels, table is $(SheetName));
NEXT;