Login form Webview disable username desktop application pkce relogin after token expiry

Hi,

On a native desktop application, webview2 control is used to show username and password. (Ref authorize call in Implement the OAuth 2.0 Authorization Code with PKCE Flow | Okta Developer)
User enters application by providing username password.
User authenticated via Oauth 2.0 pkce flow.
After a day token expires, so user is shown the login form again.
Here we want to show login form with username disabled (using same authorize call in Implement the OAuth 2.0 Authorization Code with PKCE Flow | Okta Developer), so he cannot enter credentials for another user.
We desire user enters just the valid password for login as application knows which user is currently on.

Please suggest how to disable username.

Thank you