Try this formula

=CHOOSE(Sheet1!$B$2,INDEX(FML!$B5:$G5,1,MATCH($H$4,FML!$4:$4,0)+(COLUMN(A1)-2)),
INDEX(SIC!$B5:$G5,MATCH($H$4,SIC!$4:$4,0)+(COLUMN(A1)-2)),
INDEX(GCB!$B5:$G5,1,MATCH($H$4,GCB!$4:$4,0)+(COLUMN(A1)-2)),
INDEX(GGBL!$B5:$G5,1,MATCH($H$4,GGBL!$4:$4,0)+(COLUMN(A1)-2)))