Login problem to Rocket.Chat server installed on dedicated

My customer wanted me to install Rocket.Chat server installed on his dedicated server. OS is CentOS. I was successful and it worked fine. Later customer wanted autologin if users logged in to the video upload site. It was beyond my knowledge so I advise him to hire somebody. The person he hired left the job; right now login page is not coming. http://vtubemobi.com:3000

I delete the Rocket.Chat folder in /opt and recompiled it. But login page still problematic.
When I check with “Developer Tools” I saw

Failed to load http://vtubemobi.com/api.php: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://vtubemobi.com:3000' is therefore not allowed access. 

It means that the hired guy tried authentication with http://vtubemobi.com/api.php. What should I do? Could the setting he modified be in db?