I'm not completely sure what you're asking for.

Did you accidentally send a plushie?

If so, normally you could comment to them or smail them and ask for it back. The @ link you just made would take you to their profile, or you could type https://subeta.net/users/AccioButterbeer into your browser address bar. You could also use this link to smail them (or by clicking on the big envelope on their profile).

In this case, however, I see that the user in question (AccioButterbeer) has not been on for a month. Therefore, I would also recommend filing a ticket to see if Subeta admin can help you. The link to the ticket system is here or by clicking on "Tickets" in the Subeta menu dropdown at the top of each screen. I'm not sure if they will be able to help you, but it's worth a shot to ask. :)