"Reconnect" Time Machine?

I have Time Machine backing up to a 500GB external HD. It's been faithfully backing up with no problems. A couple weeks ago the screen on my MBP died and I had to take it to the Apple Store to be fixed. I got it back today, and after setting everything up, I noticed that Time Machine hadn't backed up because it said the backup volume couldn't be located. The drive I use was connected, and mounted on the desktop, and it was listed in the TM preferences. I clicked on "change disk", re-selected it, and this time TM found it just fine, but the problem is, it's trying to create another set up backups on the HD instead of using the existing folder of backups that it's been using for months. The original set of backups were in a folder called "MacBook Pro", and now it's trying to create a new folder called "MacBook Pro 2". Is there any way to "reconnect" to the original folder that's already in place?