John Gill Commentary Leviticus 22:29

"And when ye sacrifice a sacrifice of thanksgiving unto Jehovah, ye shall sacrifice it that ye may be accepted." — Leviticus 22:29 (ASV)

And when you will offer a sacrifice of thanksgiving to the
Lord
Which was a sort of peace offering, distinct from freewill offerings and vows before spoken of:

offer [it] at your own will ;
just what they pleased, whether a bullock, a sheep, or a goat, and whether a male or female; these were left to their own option, or for acceptation to you, as the Targum of Jonathan, and so Jarchi; that is, it was right in them, and they ought to be careful to offer it in such manner, that it might be acceptable to God, by observing the rules given concerning it, particularly what follows.