declare
L_text VARCHAR2(100) := NULL;
cursor c4 is 
   select content
     from chat 
    where toid = :block3.fromid;
L_cnt NUMBER :=0;
begin

--:block3.txt_to := :parameter.p_current_user||''||':'||:block3.txt_From;

-- go_item('txt_from');

insert into chat(fromid,toid,content)values(:block3.fromid,:block3.toid,:block3.txt_From);
:block3.txt_From:= null;
commit;
:block3.txt_to := :parameter.p_current_user||''||':'||:block3.txt_From;
go_item('txt_from');

--Removed your cursor execution
for C_rec in c4
LOOP
if L_cnt = 0 then
   L_text := L_text||C_rec.content;
else
   L_text := L_text||'
'||C_rec.content;
end if;
L_cnt := L_cnt + 1;
END LOOP;
YOUR_BLOCK.YOUR_TEXT_ITEM := L_text;
end;