en_tn_condensed/2ch/25/26.md

As for the other matters ... are they not written in the book of the kings of Judah and Israel?

This rhetorical question is used to remind the reader that what happened to Amaziah is well-known. It can be translated as a statement. Alternate translation: "All of the matters concerning Amaziah, behold, are written in the book of the kings of Judah and Israel." (See: rc://en/ta/man/translate/figs-rquestion)

the other matters concerning Amaziah, first and last

Here the phrase "first and last" refers to those extremes and everything in between. Alternate translation: "all the matters concerning Amaziah" (See: rc://en/ta/man/translate/figs-merism)

behold

This alerts the reader to pay special attention to the truth of what follows.

the book of the kings of Judah and Israel

This refers to a book that no longer exists.