Thank you 
If you check your data volume for a backup and your data, these are separate, move it outside of the docker volume directory, you can simply stop & remove container, images & volume afterwards and then recreate it.
If you don’t remove your files they will be deleted when you remove the volume, you can try remove container & images first if you want but still move your data first
When it’s back up you can restore Nextcloud with the backup, move your data files back in place, use ncc to scan for external files and they will be added again
Edit: If you move your files back before you restore the backup, your files will also be deleted. Be careful