Manual writeback from docserver to nextcloud or close files


is there a feature, which I didn’t yet found that I can close all files from all users, or initiate a manual writeback to nc?
The reason is, if I am updating the docker image, all diffs/files which are placed on the document-server are lost.

As that is of course not acceptable, I ask how can I close sessions gracefully, so the users ony needs to reopen their files?.