how do i update to ios 16 when only ios 17.3 shows up

it Is my understanding that it could be done by connecting to a computer and using iTunes. If you access the Apple user’s guide you should find the solution in there. I will try and send it to you, if time permits. Good luck👍🏼

it Is my understanding that it could be done by connecting to a computer and using iTunes.

Unfortunately, your understanding is not correct. You can verify this when you find the User Guide that you mention you are looking for.

I did find an article online that relates to your question. It wasn’t in the Apple user guide, probably not wise to refer you to it. I believe that what has been said in the other posts that have responded is the best advice. 🤷‍♀️👍🏼

If iOS 17 is showing as available, it is compatible with your device. That will be your only choice.

Your phone will always update to the highest available software. No way to get around that.