Thank you for using Bitnami. I'm going to explain the steps that you need to perform to achieve this but please note that you need to be careful when following them as you can lose access to the instance. We are going to follow this section to give access to him
First of all, you will need to create new keys for that new user:
Once created, you will need to modify the users that can access the server using the bitnami account.
This is an important step, if you modify the that file and set wrong keys, you'll lose access to the instance, that's why the documentation explains the backup process.
After modifying the file, the new user can access the server using the bitnami account.
In order to access phpMyAdmin, he'll need to follow this documentation:
In case you want to remove his keys from the list with the keys that have permissions to access the server, just remove his key from the file or recover the backup file that you created in the second step.
Do not hesitate to write us back in case you have any questions.