If you weren’t verified with Uphold or Gemini, short answer is most likely you can’t. If Unverified then all Rewards were paid and stored in your browser. Therefore if you did a fresh install and didn’t have a backup of your Brave folders, then those Rewards are gone forever.
If you had been Verified with Uphold or Gemini, then they should still be there and everything fine.
Btw, it might help you to read through my FAQ as it covers many things, including Backup & Restore.