Okay, thanks for pointing out. May be you can try to use a different email address, or using a plus address (helfrd0771+lemmy[at]gmail[dot]com in your case) if you want to use the same username.
For now, plus address are treated as different as regular emails. See https://github.com/LemmyNet/lemmy/issues/3864
Ref: https://github.com/LemmyNet/lemmy-ui/issues/1096, but I suspect it's implemented or not, better to wait 24 hours before you try
If it still doesn't work, I think it is better off to reach out the admin for help.