Yes. If you write the word
it had better be a contraction of it is.
It cannot possess. You might say, “Its chew toy was a stinking mess.” Never would you say, “It’s chew toy was a stinking mess.”
Thank me later. First, go into your novels and do a ctrl-h and replace all the it’s with its, UNLESS it’s a contraction. Check each one. Universal copy and replace is going to make you sad.