Found this over on Reddit.
TL;DR; - They’ll give it to you after the next patch
Hey there,
Game Master Oughathat, checking in 
Thanks for hitting us up! I hope you’re having a great Monday, all things considered. I know these past two years have been rough for many reasons and the global pandemic is impacting our real lives as well as our online experiences. We have been working tirelessly to continue providing support to you and our other players during this time, while still taking care of each other. These efforts, along with new releases, have increased our queue times for tickets. As always, we appreciate your patience as we work on tackling the queue and replying to your ticket as soon as we can.
Speaking of your ticket, I see that you have recently reached the end of the rewards track on the Hearthstone battle pass. I completely understand the desire to sort this out.
I took a moment to investigate this and I found that we have received several reports similar to this; we are aware that some players are unable to claim the Hero Skin at the end of the Rewards Track. The issue is expected to be fixed in Patch 25.0, when players will be prompted to make their Hero Skin selection upon login. All other rewards can be claimed normally and will be automatically granted with Rewards Track swap if not claimed by that time.
Since this is a known issue, you don’t need to report this. However, if you’d like, you can add your own experience here: [Main Thread] Cannot login/claim Tavern Pass lvl 100 reward
For this and any other issues, I suggest keeping an eye on the Bug Report Forums to track known issues: https://us.forums.blizzard.com/en/hearthstone/c/bug-report/8
I appreciate your time, patience, and understanding. Please enjoy the rest of your day.
Click here to review and resolve your ticket. If you continue to experience issues, you can respond to your ticket with additional information.
If you do not resolve the ticket or provide an additional response within one week, we will resolve the ticket automatically and you’ll receive a final update via email.
Regards, Blizzard Support