This article is from the CD-Recordable FAQ, by Andy McFadden (firstname.lastname@example.org) with numerous contributions by others.
You don't. With a CD-ROM you could use multisession writes to hide
unwanted data, but you can't create multisession audio CDs. (Well, you can
create them, but nothing outside of a CD-ROM drive will be able to play the
tracks outside the first session.)
On CD-RW media, it might be possible to overwrite an individual track. You
would need software that supported this capability. Erasing the disc and
starting over is probably easier.