Lookup and return Heading of column based on criteria (sample data attached)

I just using your formula on column P and add more formula

=IFERROR(INDEX($A$1:$L$1,MATCH(IFERROR(INDEX(INDEX(A2:L2,MATCH(EOMONTH(TODAY(),-1)+1,$A$1:$L$1,0)):L2,
MATCH(1,INDEX(--(INDEX(A2:L2,MATCH(EOMONTH(TODAY(),-1)+1,$A$1:$L$1,0)):L2>0),),0)),""),A2:L2,0)),"")