daemon have write permissions in that file so you could edit it without problems.
$ ls -la /opt/bitnami/apps/redmine/htdocs/config/configuration.yml
rw-rw-r-- 1 bitnami daemon 8359 Apr 7 13:51 /opt/bitnami/apps/redmine/htdocs/config/configuration.yml
Did you modify the permissions of the Redmine's files with
chmod? Could you please let us know how you are trying to edit that file?
We have a Support Tool that will gather relevant information for us to debug the issue. Could you please download and execute it on the machine where the stack is running by following the steps described in the guide below? You must click on the platform or cloud that you are using to find the correct instructions.
How to Run the Bitnami Support Tool
Please note that you need to paste the code outputted by the tool in your reply.