Problem with formulea IF LOOKUPVALUE ?

Hi,
I would want to use a formulea to test data inside a field.
If the condition is true, I want to lookup the value from another table.
If the condition is false, I want to write a text.

I understand that Lookupvalue can return more than 1 value, but how can I change my formulea ?

Thank you,

Colonne = 
IF
(
	'public VSORDER'[VALBase]=True,
		LOOKUPVALUE(
            NbItemsInVal[NbItems], 
		    NbItemsInVal[GME],
		    'public VSORDER'[GME]
	    ), 
"Other thing"
)