For my case, I initially tried with
git config --system --unset credential.helper
But I was getting error
error: could not lock config file C:/Program Files/Git/etc/gitconfig: Permission denied
Then tried with
git config --global --unset credential.helper
No error, but still got access denied error while git pulling.
Then went to Control Panel -> Credentials Manager > Windows Credential and deleted git account.
After that when I tried git pull again, it asked for the credentials and a new git account added in Credentails manager.