I found a lot of examples on how to change the username for specific revisions and so on.
But what I need is this: I did a checkout with the authentication credentia
I’ve had the exact same problem and found the solution in Where does SVN client store user authentication data?:
cd to ~/.subversion/auth/.fgrep -l */* .(For Windows, the steps are analogous; the auth directory is in %APPDATA%\Subversion\).
Note that this will only work for SVN access schemes where the user name is part of the server login so it’s no use for repositories accessed using file://.