Zarquon
Hmm strange, have you changed the autostart option to auto login? Of course this will not work on a headless system.
However you can manually kill the running process.
When hitting Ok in the prompt, you should be able to press CTRL+C to exit the login script. Then run: htop
You should see one dietpi-login or /DietPi/dietpi/login instance running. If it indeed is hanging (0% CPU usage), then select it via up/down buttons and press F9 + return to kill it.
Then logout the SSH session and login again and you should see first run setup running on the SSH session.