Accessing Admin Dashboard (wp-admin) of Staging Site

Hello. I’m not sure how to access the admin dashboard (http://staging.example.com/wp-admin) of my staging site. I try to add wp-admin to the base of the URL and it takes me to a login screen with redirection back to my main site. I need to access my staging sites admin dashboard so I can perform actions such as edit permalink structure, install/activate plugins, customize theme, etc.