git authentication failed

Try below solution which works for me:

1: go to Windows Credential Manager. This is done in a EN-US Windows by pressing the Windows Key and typing 'credential'. In other localized Windows variants you need to use the localized term (See comments for some examples).

alternatively you can use the shortcut control /name Microsoft.CredentialManager in the run dialog (WIN+R)

2: Edit the git entry under Windows Credentials, replacing old password with the new one
Authentication failed.
You may not have permission to access the repository

Stepa to fix issue:

1.Remove repo from GitHub Desktop
2.Logout from your github account [File > Options]
3.File > Add Local Repository
4.Repository > Repository Settings and change to https URL [Important tweek]
5.It started working back for me.