What "Zichei Tzedek" should they offer?
Rashi: Make your deeds virtuous, and it is as if you offer Korbanos.
Radak: For your evil until now, you need Kaparah; offer virtuous Korbanos to Hashem - repent! Do not offer Korbanos of Resha'im - "Zevach Resha'im To'evah" (Mishlei 21:27).
Malbim: He addresses the Kohanim who offer the Korbanos that I brought (refer to 4:2:1:2).
How should they trust in Hashem?
Rashi: Trust that He will put a good influence on you, and do not sin for the sake of money, that you hope to be rewarded from Sha'ul (for informing on David).
Radak: Trust in Him, and not on your strength or great number. Trust only in Hashem. Bote'ach El is like Bote'ach Al, like "Betach El Hashem b'Chol Libecha" (Mishlei 3:5), "Al Tivtechu Lachem El Divrei Sheker" (Yirmeyah 7:4).
Malbim: Trust that he will give rain. (This was during the three years of famine.)
