Didn’t find a way other than updating the mongodb directly:
db.rocketchat_settings.updateOne( { _id: "Accounts_ShowFormLogin" }, { $set : { "value" : true } } );
This update return the default RocketChat Login Form. Once I logged in, I got message says that site url is set to localhost and asks to change. So I confirmed. Disabled default login form agian and everything is back to normal.
Not sure however why the Site URL changed to localhost by itself and how to avoid this in the future?