It is recommended to do IELTS before you apply to CIO because then you know for sure how many points you have.
You do not send your IELTS to CIO so it's not mandatory that you take it first but what has happened to some people is that they applied to CIO, took IELTS later, could not get enough points and lost their application because they ended up not having 67 or more total.
If you are certain that you can easily get the points you need on IELTS and you want to apply to CIO right away, it's your risk to take.