Currently we have a way to view tags , but I don't see a way from within Memories to add/edit/remove Nextcloud tags.
This can be done in the files app within the sidebar by clicking the three dots next to the file name:
Perhaps Memories can implement this functionality?
IMO, the three dot menu just for tags is a poor design choice, but if that's how Nextcloud does it, then Memories should probably implement it the same way for consistency (if you want to implement this at all).