Can't use password in Kali Linux after changing username

I decided to change the username of my kali linux to a new one so I did the following commands :
changed both old_username (kali) to new_username (xyz) :

Code:

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sudo nano /etc/passwd

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but when I did this one, I got "Sorry, try again." and finally "sudo: 3 incorrect password attempts"

Code:

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sudo mv /home/kali/ /home/celsius/

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Then I tried to go back to revert to old_username but I was locked out for writing on the file...

Code:

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sudo nano /etc/passwd

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That's when I figured out that I change the username but not the name of the home folder meaning it doesn't know where to look for my settings... Tried to login as root but don't know how either
Can you help me please ? Thanks