This would be useful if, for example, your password has been reset by an SDUI admin and you now want to enter your personal password.
Go to the app settings via the drop-down menu at the top right and select the top tile "Change my profile, school data & passwords".
Scroll down until you find the line "Password" and click on "Change" to the right of it. You will now be asked to enter your previous password and then set the new password.
As soon as you click on "Save", the change of your password is complete.