bibtex-yank-pop is an interactive compiled Lisp function in `bibtex.el'.

(bibtex-yank-pop N)

Replace just-yanked killed BibTeX item with a different item.
This command is allowed only immediately after a `bibtex-yank' or a
`bibtex-yank-pop'. In this case, the region contains a reinserted
previously killed BibTeX item. `bibtex-yank-pop' deletes that item
and inserts in its place a different killed BibTeX item.

With no argument, the previous kill is inserted.
With argument N, insert the Nth previous kill.
If N is negative, this is a more recent kill.

The sequence of kills wraps around, so that after the oldest one
comes the newest one.