Thanks all for your advices. The bike is OK. Only pain scratch where the brake arm hit the downtube (thanks to the tiny rubber ring of cable adjuster).
I can't see the bend on the arm itself. only the space between rim and brake pad indicate there is a change in aligment between brake bolt hole and brake pad end.
I just don't know if the heat would help or necessary to stabilized the bent.
I we worry too much about safety then we should not buy any used bike and that not the case for us CVer!!!