=if(INDEX('Rota April to July'!$A$7:$A$1000,MATCH($B5,'Rota April to July'!$C$7:$C$1000,0))="",
INDEX('Rota April to July'!$A$7:$A$1000,MATCH($B5,'Rota April to July'!$D$7:$D$1000,0)),
INDEX('Rota April to July'!$A$7:$A$1000,MATCH($B5,'Rota April to July'!$C$7:$C$1000,0))
seems long i know, there may be a better way