Otherwise you have to do it on request, either by email or form submission or link; automated or manually as you will have 24 hours to follow through with the request. I'd keep track of these requests just in case you need to restore a backup where their data still exists, to notify them and delete their data again from the backup.
...but really, no idea. Im likely just going to put a contact form in and handle any requests manually.
I would like to extend the question by asking the owners of event-sourced systems how they handle it.
In my case, we will have to do manuell, software-assisted deletions
I don't use any piece of shit like Google Analytics, or tracking services, so that's already a plus.
I don't collect anything I don't explictly need on my users, it's easier to manager, more secure and will make it easier to handle those new laws.
From backups too...
You just need a process in place so you don't restore those same users if ever restoring backups.
Different strokes I suppose.
Can we agree at least that you have to account for deletion in your backup strategy?
In the rare event you restore deleted users, and even rarer, if they actually notice, just tell them you screwed up.