Welcome to the Apple Support Communities
Time Machine doesn't erase old backups. That's only done when your Time Machine disk or Time Capsule gets full.
If you want to mean that you have connected the Time Capsule to another Mac to create another Time Machine backup, you should know that the old backup isn't modified, and you can still restore files from that old backup > http://pondini.org/TM/E3.html
If you saw a message that Time Machine was going to create a new backup, that means the old backup set was corrupt and had to be completely replaced. It can't be recovered. You always need more than one backup to be safe, especially if you back up over a network, which is less reliable than backing up to a local storage device.