Lookup in Reports BI Report Builder

[Garbo62]

Hi

 In Reports BI Report Builder (First time ever using it) I want to bring in ACat2Desc in to table A_TYPE where  ACat2Desc is in table  A_CAT2 where the common connector is ACAT2UID and GPE_A_CAT2

When I try to build the query if defaults to this

=Lookup(Fields!GPE_A_CAT2.Value, First(Fields!ACat2UID.Value, "A_CAT2"), First(Fields!ACat2Desc.Value, "A_CAT2")

What is the correct Syntex to link /pull data in to the table