Using the new installed (7.5.4 GP) I clicked the burger menu (left), then user icon (right to the gear).
=> Message: No user logged in
Continue with Registration => login => E-Mail (select my email address)
Then leave the password field empty, and click on the large button at the bottom of the page "Passwort Speichern" (German translation, in English Save Password).
Then I got the message (New password sent to your email.) That worked fine
But I got to this soluion by accident. Maybe the root cause of the difficulty is just a wrong English=>German translation of the button "Passwort Speichern"?