WordPress user_nicename Problem

I change and confirm ‘user_nicename’ from the table in cPanel> phpMyAdmin> (Related Web Page) user> Edit. There is no problem. However, the user_nicename I created always adds ‘-2’ to the end. For example, if I set the user_nicename as wordpress and save it, after a while it looks like this on the web page: ‘wordpress-2’. This is the case (wordpress-2-2-2 -…) What is the reason for this? How can I solve this problem? Note: The user_nicename I want to use is the user_nicename I used earlier. So I want to use the first one. Also there is no other user using it.
More, i can get this user_nicename on a new registration. No problem. However, as I said at the beginning, if I get this as admin, it adds (wordpress-2-2-2 …). How can I solve this problem?