HTTP 302 means redirection. That means that, somehow, apache is set up so that when ELB is making requests to your URL, it is sending you somewhere else.
What you should do is to make it point to an existing file in your prestashop set up. I have checked myself, and
curl -I http://IP_OF_PRESTASHOP_INSTALLATION/
does return the desired 200 OK response. I don't understand from your request whether you tried with that, but, if not, could you please try?
If you are still getting those 302 responses, then it's likely that the apache configuration has been somehow affected. If that is the case, then you should try checking the apache logs (files at
/opt/bitnami/apache2/logs/) and attaching them here, so we can see where are you being redirected.
We’ll be looking forward to receiving your reply.