psql：FATAL：尝试访问psql时，用户错误的密码身份验证失败

I am using Windows 10 and just installed Psql (9.6.4) for it. While installing, it asked me to enter password for the superuser 'postgres' which i entered lets say, 'asdfasdf'. So after installing, I check the version with I am using Windows 10 and just installed Psql (