how to purge the list of backups still availables?

Hi all, one external hard disk where I do the full backup is broken, lost everything, but there is no problem, had the backups already very old.
The problem is that if I try to retrieve a file via the Restore job, I still see as available backups made on that hard drive.

Question: How do I delete all backups made on that disk and that are listed as still available?

I use BEX 2010 SP3 Rev. 5204 on Windows 2008 Srv Std 64b.

Thanks.