I have three external hard drives listed with my Time Machine backup. I no longer use these drives. How do I get them removed as being used for time machine backups?

I previously had three external hard drives that I have used to backup my mac using Time Machine. Over time, each one of these external drives has failed. They are still listed as being the drives used for Time Machine backups.

1. How do I remove them from being listed?
2. While in Time Machine, the new external hard drive which has been partitioned and formatted as Mac OS Extended (Journaled & Encrypted) is not found and I am not asked to set this as the new backup disk. How can I set it up as the new backup?

Thanks