This article explains how to attach a new volume to a running container. This operation destroys the running container and starts a new one with the volume attached.
Always back up your data before running this operation.
From the menu select Containers, select the container that you want to attach a volume to, then click Duplicate/Edit.
Scroll down to Advanced container settings. Click Volumes then click map additional volume.
In the container field enter the path. In the volume field enter the volume to attach to the container.
When you're ready, click Deploy the container. When the confirmation message appears, click Replace.