Installing WordPress on a Subdomain

First off, a little back story. I am a Graphic Designer and typically do not handle any form of website management, but I got a call from someone basically begging me to help get their site up and running. They have a completed website built by an outside developer that was nearly 100% complete with the exception of a few products added, unfortunately, the man fell ill with cancer and was unable to finish the project. He had packed up the entire website from the wordpress files, the database and any plugins used. He gave me instructions on how to get the site up on my clients server.

My client has commercialcarpeting.net as his domain. He does not want to take the website down until we finish adding product to his new website. To remedy this, I made a subdomain test.commercialcarpeting.net and uploaded all of the website files there. I created a new database and uploaded all necessary files. I edited the wp-config file with the new database credentials. Upon initially traveling to the domain, it prompted me that wp-config already exists to begin installation. After clicking begin installation, it says wordpress is already installed, now all it does it redirect me from test.commercialcarpeting. net to commercialcarpeting.net…

Does anyone have a solution I can try? I am somewhat familiar with FTP as I use it quite a bit updating our website at the company I work. I have very limited wordpress experience.

Thanks,
Spencer