Thank you for all the answers and comments.
I’m a little confused too.
My Jolla login name was not identical to the username displayed in the old forum.
Of course I had to log in to the forum using the Jolla account with the Jolla username, but I was able to change the name displayed in the forum.
In order to enable an assignment of my person to the old forum, it would be helpful if I could also set this up here so that other users can also assign me.
As far as I understand it, a change here is not possible.
I can only add my “old” username as a name.
I beg your pardon for the confusion caused.