How can I get back TikTok on iPhone?

You won't be able to get it back. Google users are in the same boat too as it is not in the Google Play Store either. The reason is that Congress placed fines on both companies if they allow anyone to download or redownload the app. It makes no difference if you had it before, you still cannot redownload it.

Bummer.

IMPORTANT UPDATE:

The TikTok app has returned to the App Store.

Good luck! 👋🏼😉

Nope. Not happening. At least not until and unless ByteDance sells TikTok to a non Chinese owner.