Hello, you will be able to download the Tik Tok app on the Tizen Store, once it is available.
For the time being the Tik Tok app has not yet been uploaded to the Tizen Store, however it would appear that with Tik Tok's increasing popularity it should be available soon.
There is still nothing official from either TikTok or Samsung about the app coming to the Tizen Store. Look on their respective websites for more info, and maybe consider contacting their teams directly.