Hi Jagjot,
Open Computer Management > Local users and Groups > User > then you will find the account that you created under Kiosk mode - just delete that. Then check if you could remove kiosk.
If this method failed, try to enter WinRE by a installation media, restore system or reset this PC.
Check this similar case for some ideas.
Assigned Access will not start - Microsoft Q&A
https://learn.microsoft.com/en-us/answers/questions/204877/assigned-access-will-not-start.html
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