I accidentally sold irisviel

Usually I'd say wait for the re-run, but this event has yet to have one. Looks like you gotta keep your fingers crossed.
At least you'll always remember to lock your gold servants as soon as you get them from now on?

You can get 5 copies of Irisviel in the event, so you can get her to NP5. So in your case that will be only NP4. Be more careful next time, I guess.
You can try contacting support. I have no idea if you will be able to get her back.

Sorry bro, once it's gone, It's really gone. There's no way to bring that 1 irisviel back. I don't think support can help you, but it doesn't hurt to just try

Just don't use servants to lvl up other servants. Is a waste of QP.