Ok, this is unfortunately a little complex.
The easiest way to do things is probably to uninstall PostgreSQL completely, remove the new directory that was created that had very little to no new data in it - move your database backup into place. Download and install PostgreSQL from
this link, when you get to the section, uncheck Initialize Database Cluster (it should say a database cluster was located in the directory you chose), and finish the install. Hopefully the database will start up - if it doesn't, we'll need to inspect logs to see why not.