When I open YouTube my Galaxy S8 restart it self so can you help what can i do ?

I also shut down my phone and i clear the whole history and see if there is a various but it's the same

Welcome to Android Central! Does this happen in Safe Mode as well? https://support.t-mobile.com/docs/DOC-34283. Does the phone reboot randomly when using any other app, or is it always YouTube?

Have you also tried going to the App Manager, selecting YouTube, and clearing the cache/data?