try this:
data wanted;
set test;
length bangong $20;
retain n;
array item{*} item:;
if mod(_n_,2)=1 then do;
n=.;
do i=1 to dim(item);
if index(item{i},'AAA') then do;
bangong=item{i};
n=i;
end;
end;
end;
if mod(_n_,2)=0 and n ne . then bangong=item{n};
drop i n;
run;