If you want 01/09/2019 from 01/03/2019 then use Paul's example -
{QUOTE {SET NoticeDate{MERGEFIELD Unit_Lease_Dates8}} {SET Delay {MERGEFIELD Unit_Lease_Dates_Notice6}} {SET mm{=MOD(ABS({NoticeDate \@ M}+Delay+11),12)+1}} {SET yy{=INT({NoticeDate \@ yyyy}+(Delay+{DATE \@ M}-1)/12)}} {SET dd{=IF(({NoticeDate \@ d}>28)*(mm=2)=1,28+((MOD(yy,4)=0)+(MOD(yy,400)=0)-(MOD(yy,100)=0)),IF((mm=4)+(mm=6)+(mm=9)+(mm=11)+( {NoticeDate \@ d}>30)>1,30,{NoticeDate \@ d}))}} "{dd}-{mm}-{yy}" \@ "dddd, d MMMM yyyy"}
Change the final switch \@ "dddd, d MMMM yyyy" to \@ "dd/MM/yyyy"
and then so you don't screw it up, use
www.gmayor.com/export_field.htm to convert the text listing to fields.