You can create immediately a (new) personal password.
Please choose for this purpose on the welcome screen the option 'Log in with password', click at the bottom of the screen on the hyperlink 'I want to create or modify my password' and then just follow the instructions.
For your own safety we recommend you to keep your user number and your personal password strictly separately and in safe locations.
After having created a personal password, you can always log in with itsme®.