a2enmod won't work because the Apache modules aren't part of your system, they are placed in a specific folder under the Bitnami installation folder at
/opt/bitnami. Can you try to run the command below to check if the rewrite module is loaded on your Apache server?
/opt/bitnami/apache2/bin/apachectl -M | grep rewrite
Output on my server is shown below, so it means that the module is loaded.
$ apachectl -M | grep rewrite
If your output is not the same, try to restart services
sudo /opt/bitnami/ctlscript.sh restart