How do I get TikTok back on iPhone?

No.

TikTok has been banned by the US. government and therefore it will not be available in the US. until the ban has been lifted.

About availability of TikTok and ByteDance Ltd. apps in the United States - Apple Support

How can you get TikTok on your iPhone pls tell me how

IMPORTANT UPDATE:

The TikTok app has returned to the App Store.

Good luck! 👋🏼😉

Birian wrote:

How can you get TikTok on your iPhone pls tell me how

You don't. That is an easy one.