You can claim it via the Samsung Boost website - https://www.samsung.com/uk/boost if you're in the UK. Sign in with the same Samsung account you used to set up your tablet and the offer (as well as a few other offers) will be on the front page. I also think you need to use your S8 when visiting that website.
Thanks for that! Nothing was stated anywhere that you should use the new tablet to login to make the claim. I have now made the claim and got it setup on my TV and S8. I really appreciate you taking the time to post the reply, wish I had thought about the members site sooner, would have saved me a lot of grief.